Systems and methods for applying deblocking filters to reconstructed video data

ABSTRACT

This disclosure relates to video coding and more particularly to techniques for performing deblocking of reconstructed video data. In one example, a method of filtering reconstructed video data is disclosed. The method comprises: receiving an edge type variable specifying whether a vertical or horizontal edge is filtered; deriving a maximum filter length based on the edge type variable; and performing a deblocking filtering for a current block based on the maximum filter length.

CLAIM OF BENEFIT TO PRIOR APPLICATIONS

This application is a national stage application of International Patent Application PCT/JP2019/043978, filed Nov. 8, 2019, now published as WO2020/100764. International Patent Application PCT/JP2019/043978 claims the benefit of U.S. Provisional Patent Applications 62/767,362, filed Nov. 14, 2018; 62/790,917, filed Jan. 10, 2019; and 62/793,844, filed Jan. 17, 2019. U.S. Provisional Patent Applications 62/767,362, 62/790,917, and 62/793,844, and International Patent Application PCT/JP2019/043978, now published as WO2020/100764, are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to video coding and more particularly to techniques for performing deblocking of reconstructed video data.

BACKGROUND ART

Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, laptop or desktop computers, tablet computers, digital recording devices, digital media players, video gaming devices, cellular telephones, including so-called smartphones, medical imaging devices, and the like. Digital video may be coded according to a video coding standard. Video coding standards may incorporate video compression techniques. Examples of video coding standards include ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC) and High-Efficiency Video Coding (HEVC). HEVC is described in High Efficiency Video Coding (HEVC), Rec. ITU-T H.265, December 2016, which is incorporated by reference, and referred to herein as ITU-T H.265. Extensions and improvements for ITU-T H.265 are currently being considered for the development of next generation video coding standards. For example, the ITU-T Video Coding Experts Group (VCEG) and ISO/IEC (Moving Picture Experts Group (MPEG) (collectively referred to as the Joint Video Exploration Team (JVET)) are studying the potential need for standardization of future video coding technology with a compression capability that significantly exceeds that of the current HEVC standard. The Joint Exploration Model 7 (JEM 7), Algorithm Description of Joint Exploration Test Model 7 (JEM 7), ISO/IEC JTC1/SC29/WG11 Document: JVET-G1001, July 2017, Torino, I T, which is incorporated by reference herein, describes the coding features that are under coordinated test model study by the JVET as potentially enhancing video coding technology beyond the capabilities of ITU-T H.265. It should be noted that the coding features of JEM 7 are implemented in JEM reference software. As used herein, the term JEM may collectively refer to algorithms included in JEM 7 and implementations of JEM reference software.

Video compression techniques reduce data requirements for storing and transmitting video data by exploiting the inherent redundancies in a video sequence. Video compression techniques may sub-divide a video sequence into successively smaller portions (i.e., groups of frames within a video sequence, a frame within a group of frames, slices within a frame, coding tree units (e.g., macroblocks) within a slice, coding blocks within a coding tree unit, etc.). Intra prediction coding techniques (e.g., intra-picture (spatial)) and inter prediction techniques (i.e., inter-picture (temporal)) may be used to generate difference values between a unit of video data to be coded and a reference unit of video data. The difference values may be referred to as residual data. Residual data may be coded as quantized transform coefficients. Syntax elements may relate residual data and a reference coding unit (e.g., intra-prediction mode indices, motion vectors, and block vectors). Residual data and syntax elements may be entropy coded. Entropy encoded residual data and syntax elements may be included in a compliant bitstream. Compliant bitstreams and associated metadata may be formatted according to data structures.

SUMMARY OF INVENTION

In one example, a method of filtering reconstructed video data, the method comprising: receiving an edge type variable specifying whether a vertical or a horizontal edge is filtered; deriving a maximum filter length based on the edge type variable; and performing a deblocking filtering for a current block based on the maximum filter length.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example of a group of pictures coded according to a quad tree binary tree partitioning in accordance with one or more techniques of this disclosure.

FIG. 2 is a conceptual diagram illustrating an example of a video component sampling format in accordance with one or more techniques of this disclosure.

FIG. 3 is a conceptual diagram illustrating possible coding structures for a block of video data in accordance with one or more techniques of this disclosure.

FIG. 4A is a conceptual diagram illustrating example of coding a block of video data in accordance with one or more techniques of this disclosure.

FIG. 4B is a conceptual diagram illustrating example of coding a block of video data in accordance with one or more techniques of this disclosure.

FIG. 5A is a conceptual diagram illustrating block of video data including a deblocking boundary in accordance with one or more techniques of this disclosure.

FIG. 5B is a conceptual diagram illustrating block of video data including a deblocking boundary in accordance with one or more techniques of this disclosure.

FIG. 6A is an example of a table that may be used to determine deblocking parameters in accordance with one or more techniques of this disclosure.

FIG. 6B is an example of a table that may be used to determine deblocking parameters in accordance with one or more techniques of this disclosure.

FIG. 7 is a block diagram illustrating an example of a system that may be configured to encode and decode video data according to one or more techniques of this disclosure.

FIG. 8 is a block diagram illustrating an example of a video encoder that may be configured to encode video data according to one or more techniques of this disclosure.

FIG. 9 is a block diagram illustrating an example of a video decoder that may be configured to decode video data according to one or more techniques of this disclosure.

FIG. 10 is a flowchart illustrating an example of performing deblocking according to one or more techniques of this disclosure.

FIG. 11 is a flowchart illustrating an example of performing deblocking according to one or more techniques of this disclosure.

FIG. 12 is a flowchart illustrating an example of performing deblocking according to one or more techniques of this disclosure.

FIG. 13 is an example of a table that may be used to determine deblocking parameters in accordance with one or more techniques of this disclosure.

FIG. 14A is a conceptual diagram illustrating block of video data including a deblocking boundary in accordance with one or more techniques of this disclosure.

FIG. 14B a conceptual diagram illustrating block of video data including a deblocking boundary in accordance with one or more techniques of this disclosure.

DESCRIPTION OF EMBODIMENTS

In general, this disclosure describes various techniques for coding video data. In particular, this disclosure describes techniques for performing deblocking of reconstructed video data. It should be noted that although techniques of this disclosure are described with respect to ITU-T H.264, ITU-T H.265, and JEM, the techniques of this disclosure are generally applicable to video coding. For example, the coding techniques described herein may be incorporated into video coding systems, (including video coding systems based on future video coding standards) including block structures, intra prediction techniques, inter prediction techniques, transform techniques, filtering techniques, and/or entropy coding techniques other than those included in ITU-T H.265. Thus, reference to ITU-T H.264, ITU-T H.265 and JEM is for descriptive purposes and should not be construed to limit the scope of the techniques described herein. Further, it should be noted that incorporation by reference of documents herein should not be construed to limit or create ambiguity with respect to terms used herein. For example, in the case where an incorporated reference provides a different definition of a term than another incorporated reference and/or as the term is used herein, the term should be interpreted in a manner that broadly includes each respective definition and/or in a manner that includes each of the particular definitions in the alternative.

In one example, a method of filtering reconstructed video data comprises receiving an array of sample values including adjacent reconstructed video blocks for a component of video data, and modifying sample values in the adjacent reconstructed video blocks according to multiple passes of a deblocking filter.

In one example, a device for video coding comprises one or more processors configured to receive an array of sample values including adjacent reconstructed video blocks for a component of video data, and modify sample values in the adjacent reconstructed video blocks according to multiple passes of a deblocking filter.

In one example, a non-transitory computer-readable storage medium comprises instructions stored thereon that, when executed, cause one or more processors of a device to receive an array of sample values including adjacent reconstructed video blocks for a component of video data, and modify sample values in the adjacent reconstructed video blocks according to multiple passes of a deblocking filter.

In one example, an apparatus comprises means for receiving an array of sample values including adjacent reconstructed video blocks for a component of video data, and means for modifying sample values in the adjacent reconstructed video blocks according to multiple passes of a deblocking filter.

The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

Video content typically includes video sequences comprised of a series of frames. A series of frames may also be referred to as a group of pictures (GOP). Each video frame or picture may include a plurality of slices or tiles, where a slice or tile includes a plurality of video blocks. As used herein, the term video block may generally refer to an area of a picture or may more specifically refer to the largest array of sample values that may be predictively coded, sub-divisions thereof, and/or corresponding structures. Further, the term current video block may refer to an area of a picture being encoded or decoded. A video block may be defined as an array of sample values that may be predictively coded. It should be noted that in some cases pixel values may be described as including sample values of respective components of video data, which may also be referred to as color components, (e.g., luma (Y) and chroma (Cb and Cr) components or red, green, and blue components). It should be noted that in some cases, the terms pixel values and sample values are used interchangeably. Video blocks may be ordered within a picture according to a scan pattern (e.g., a raster scan). A video encoder may perform predictive encoding on video blocks and sub-divisions thereof. Video blocks and sub-divisions thereof may be referred to as nodes.

ITU-T H.264 specifies a macroblock structure including 16×16 luma samples. That is, in ITU-T H.264, a picture is segmented into macroblocks. ITU-T H.265 specifies an analogous Coding Tree Unit (CTU) structure, which may also be referred to as a largest coding unit (LCU). In ITU-T H.265, pictures are segmented into CTUs. In ITU-T H.265, for a picture, a CTU size may be set as including 16×16, 32×32, or 64×64 luma samples. In ITU-T H.265, a CTU is composed of respective Coding Tree Blocks (CTB) for each component of video data (e.g., luma (Y) and chroma (Cb and Cr)). Further, in ITU-T H.265, a CTU may be partitioned according to a quadtree (QT) partitioning structure, which results in the CTBs of the CTU being partitioned into Coding Blocks (CB). That is, in ITU-T H.265, a CTU may be partitioned into quadtree leaf nodes. According to ITU-T H.265, one luma CB together with two corresponding chroma CBs and associated syntax elements are referred to as a coding unit (CU). In ITU-T H.265, a minimum allowed size of a CB may be signaled. In ITU-T H.265, the smallest minimum allowed size of a luma CB is 8×8 luma samples. In ITU-T H.265, the decision to code a picture area using intra prediction or inter prediction is made at the CU level.

In ITU-T H.265, a CU is associated with a prediction unit (PU) structure having its root at the CU. In ITU-T H.265, PU structures allow luma and chroma CBs to be split for purposes of generating corresponding reference samples. That is, in ITU-T H.265, luma and chroma CBs may be split into respect luma and chroma prediction blocks (PBs), where a PB includes a block of sample values for which the same prediction is applied. In ITU-T H.265, a CB may be partitioned into 1, 2, or 4 PBs. ITU-T H.265 supports PB sizes from 64×64 samples down to 4×4 samples. In ITU-T H.265, square PBs are supported for intra prediction, where a CB may form the PB or the CB may be split into four square PBs (i.e., intra prediction PB size types include M×M or M/2×M/2, where M is the height and width of the square CB). In ITU-T H.265, in addition to the square PBs, rectangular PBs are supported for inter prediction, where a CB may by halved vertically or horizontally to form PBs (i.e., inter prediction PB types include M×M, M/2×M/2, M/2×M, or M×M/2). Further, it should be noted that in ITU-T H.265, for inter prediction, four asymmetric PB partitions are supported, where the CB is partitioned into two PBs at one quarter of the height (at the top or the bottom) or width (at the left or the right) of the CB (i.e., asymmetric partitions include M/4×M left, M/4×M right, M×M/4 top, and M×M/4 bottom). Intra prediction data (e.g., intra prediction mode syntax elements) or inter prediction data (e.g., motion data syntax elements) corresponding to a PB is used to produce reference and/or predicted sample values for the PB.

JEM specifies a CTU having a maximum size of 256×256 luma samples. JEM specifies a quadtree plus binary tree (QTBT) block structure. In JEM, the QTBT structure enables quadtree leaf nodes to be further partitioned by a binary tree (BT) structure. That is, in JEM, the binary tree structure enables quadtree leaf nodes to be recursively divided vertically or horizontally. FIG. 1 illustrates an example of a CTU (e.g., a CTU having a size of 256×256 luma samples) being partitioned into quadtree leaf nodes and quadtree leaf nodes being further partitioned according to a binary tree. That is, in FIG. 1 dashed lines indicate additional binary tree partitions in a quadtree. Thus, the binary tree structure in JEM enables square and rectangular leaf nodes, where each leaf node includes a CB. As illustrated in FIG. 1 , a picture included in a GOP may include slices, where each slice includes a sequence of CTUs and each CTU may be partitioned according to a QTBT structure. FIG. 1 illustrates an example of QTBT partitioning for one CTU included in a slice. Thus, the binary tree structure in JEM enables square and rectangular leaf nodes, where each leaf node includes a CB. In JEM, CBs are used for prediction without any further partitioning. That is, in JEM, a CB may be a block of sample values on which the same prediction is applied. Thus, a JEM QTBT leaf node may be analogous a PB in ITU-T H.265.

A video sampling format, which may also be referred to as a chroma format, may define the number of chroma samples included in a CU with respect to the number of luma samples included in a CU. For example, for the 4:2:0 sampling format, the sampling rate for the luma component is twice that of the chroma components for both the horizontal and vertical directions. As a result, for a CU formatted according to the 4:2:0 format, the width and height of an array of samples for the luma component are twice that of each array of samples for the chroma components. FIG. 2 is a conceptual diagram illustrating an example of a coding unit formatted according to a 4:2:0 sample format. FIG. 2 illustrates the relative position of chroma samples with respect to luma samples within a CU. As described above, a CU is typically defined according to the number of horizontal and vertical luma samples. Thus, as illustrated in FIG. 2 , a 16×16 CU formatted according to the 4:2:0 sample format includes 16×16 samples of luma components and 8×8 samples for each chroma component. Further, in the example illustrated in FIG. 2 , the relative position of chroma samples with respect to luma samples for video blocks neighboring the 16×16 CU are illustrated. For a CU formatted according to the 4:2:2 format, the width of an array of samples for the luma component is twice that of the width of an array of samples for each chroma component, but the height of the array of samples for the luma component is equal to the height of an array of samples for each chroma component. Further, for a CU formatted according to the 4:4:4 format, an array of samples for the luma component has the same width and height as an array of samples for each chroma component.

As described above, intra prediction data or inter prediction data is used to produce reference sample values for a block of sample values. The difference between sample values included in a current PB, or another type of picture area structure, and associated reference samples (e.g., those generated using a prediction) may be referred to as residual data. Residual data may include respective arrays of difference values corresponding to each component of video data. Residual data may be in the pixel domain. A transform, such as, a discrete cosine transform (DCT), a discrete sine transform (DST), an integer transform, a wavelet transform, or a conceptually similar transform, may be applied to an array of difference values to generate transform coefficients. It should be noted that in ITU-T H.265, a CU is associated with a transform unit (TU) structure having its root at the CU level. That is, in ITU-T H.265, an array of difference values may be sub-divided for purposes of generating transform coefficients (e.g., four 8×8 transforms may be applied to a 16×16 array of residual values). For each component of video data, such sub-divisions of difference values may be referred to as Transform Blocks (TBs). It should be noted that in ITU-T H.265, TBs are not necessarily aligned with PBs. FIG. 3 illustrates examples of alternative PB and TB combinations that may be used for coding a particular CB. Further, it should be noted that in ITU-T H.265, TBs may have the following sizes 4×4, 8×8, 16×16, and 32×32. In JEM, residual values corresponding to a CB are used to generate transform coefficients without further partitioning. That is, in JEM a QTBT leaf node may be analogous to both a PB and a TB in ITU-T H.265. It should be noted that in JEM, a core transform and a subsequent secondary transforms may be applied (in the video encoder) to generate transform coefficients. For a video decoder, the order of transforms is reversed. Further, in JEM, whether a secondary transform is applied to generate transform coefficients may be dependent on a prediction mode.

Transform coefficients may be quantized according to a quantization process. Quantization approximates transform coefficients by amplitudes restricted to a set of specified values. Quantization may be used in order to vary the amount of data required to represent a group of transform coefficients. Quantization may be generally described as being realized through division of transform coefficients by a scaling factor and any associated rounding functions (e.g., rounding to the nearest integer). Thus, inverse quantization (or “dequantization”) may include multiplication of coefficient level values by the scaling factor. It should be noted that as used herein the term quantization process in some instances may generally refer to division by a scaling factor to generate level values or multiplication by a scaling factor to recover transform coefficients in some instances. That is, a quantization process may refer to quantization in some cases and inverse quantization in some cases. A current block of video data is reconstructed by performing inverse quantization on level values, performing an inverse transform, and adding a set of prediction values to the resulting residual. The sample values of the reconstructed block may differ from the sample values of the current video block that were input into an encoding process. In this manner, coding may be said to be lossy. However, it should be noted that the difference in sample values may be considered acceptable to a viewer of the reconstructed video.

Quantized transform coefficients (which may be referred to as level values) may be entropy coded according to an entropy encoding technique (e.g., content adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), probability interval partitioning entropy coding (PIPE), etc.). Further, syntax elements, such as, a syntax element indicating a prediction mode, may also be entropy coded. Entropy encoded quantized transform coefficients and corresponding entropy encoded syntax elements may form a compliant bitstream that can be used to reproduce video data. A binarization process may be performed on syntax elements as part of an entropy coding process. Binarization refers to the process of converting a syntax value into a series of one or more bits. These bits may be referred to as “bins.”

FIGS. 4A-4B are conceptual diagrams illustrating examples of coding a block of video data. As illustrated in FIG. 4A, a current block of video data (e.g., a CB corresponding to a video component) is encoded by generating a residual by subtracting a set of prediction values from the current block of video data, performing a transformation on the residual, and quantizing the transform coefficients to generate level values. As illustrated in FIG. 4B, the current block of video data is decoded by performing inverse quantization on level values, performing an inverse transform, and adding a set of prediction values to the resulting residual. It should be noted that in the examples in FIGS. 4A-4B, the sample values of the reconstructed block differs from the sample values of the current video block that is encoded. In this manner, coding may said to be lossy. However, the difference in sample values may be considered acceptable or imperceptible to a viewer of the reconstructed video.

As illustrated in FIG. 4A, quantized transform coefficients are coded into a bitstream. Quantized transform coefficients and syntax elements (e.g., syntax elements indicating a coding structure for a video block) may be entropy coded according to an entropy coding technique. Examples of entropy coding techniques include content adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), probability interval partitioning entropy coding (PIPE), and the like. Entropy encoded quantized transform coefficients and corresponding entropy encoded syntax elements may form a compliant bitstream that can be used to reproduce video data at a video decoder. An entropy coding process may include performing a binarization on syntax elements. Binarization refers to the process of converting a value of a syntax value into a series of one or more bits. These bits may be referred to as “bins.” Binarization is a lossless process and may include one or a combination of the following coding techniques: fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding. For example, binarization may include representing the integer value of 5 for a syntax element as 00000101 using an 8-bit fixed length binarization technique or representing the integer value of 5 as 11110 using a unary coding binarization technique. As used herein each of the terms fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding may refer to general implementations of these techniques and/or more specific implementations of these coding techniques. For example, a Golomb-Rice coding implementation may be specifically defined according to a video coding standard, for example, ITU-T H.265. An entropy coding process further includes coding bin values using lossless data compression algorithms. In the example of a CABAC, for a particular bin, a context model may be selected from a set of available context models associated with the bin. In some examples, a context model may be selected based on a previous bin and/or values of previous syntax elements. A context model may identify the probability of a bin having a particular value. For instance, a context model may indicate a 0.7 probability of coding a 0-valued bin and a 0.3 probability of coding a 1-valued bin. It should be noted that in some cases the probability of coding a 0-valued bin and probability of coding a 1-valued bin may not sum to 1. After selecting an available context model, a CABAC entropy encoder may arithmetically code a bin based on the identified context model. The context model may be updated based on the value of a coded bin. The context model may be updated based on an associated variable stored with the context, e.g., adaptation window size, number of bins coded using the context. It should be noted, that according to ITU-T H.265, a CABAC entropy encoder may be implemented, such that some syntax elements may be entropy encoded using arithmetic encoding without the usage of an explicitly assigned context model, such coding may be referred to as bypass coding.

As described above, intra prediction data or inter prediction data may associate an area of a picture (e.g., a PB or a CB) with corresponding reference samples. For intra prediction coding, an intra prediction mode may specify the location of reference samples within a picture. In ITU-T H.265, defined possible intra prediction modes include a planar (i.e., surface fitting) prediction mode (predMode: 0), a DC (i.e., flat overall averaging) prediction mode (predMode: 1), and 33 angular prediction modes (predMode: 2-34). In JEM, defined possible intra-prediction modes include a planar prediction mode (predMode: 0), a DC prediction mode (predMode: 1), and 65 angular prediction modes (predMode: 2-66). It should be noted that planar and DC prediction modes may be referred to as non-directional prediction modes and that angular prediction modes may be referred to as directional prediction modes. It should be noted that the techniques described herein may be generally applicable regardless of the number of defined possible prediction modes.

For inter prediction coding, a motion vector (MV) identifies reference samples in a picture other than the picture of a video block to be coded and thereby exploits temporal redundancy in video. For example, a current video block may be predicted from reference block(s) located in previously coded frame(s) and a motion vector may be used to indicate the location of the reference block. A motion vector and associated data may describe, for example, a horizontal component of the motion vector, a vertical component of the motion vector, a resolution for the motion vector (e.g., one-quarter pixel precision, one-half pixel precision, one-pixel precision, two-pixel precision, four-pixel precision), a prediction direction and/or a reference picture index value. Further, a coding standard, such as, for example ITU-T H.265, may support motion vector prediction. Motion vector prediction enables a motion vector to be specified using motion vectors of neighboring blocks. Examples of motion vector prediction include advanced motion vector prediction (AMVP), temporal motion vector prediction (TMVP), so-called “merge” mode, and “skip” and “direct” motion inference. Further, JEM supports advanced temporal motion vector prediction (ATMVP), Spatial-temporal motion vector prediction (STMVP), Pattern matched motion vector derivation (PMMVD) mode, which is a special merge mode based on Frame-Rate Up Conversion (FRUC) techniques, and affine transform motion compensation prediction techniques.

As described above, quantization may be realized through division of transform coefficients by a scaling factor and further may be used in order to vary the amount of data required to represent a group of transform coefficients. That is, increasing the scaling factor (or degree of quantization) reduces the amount of data required to represent a group coefficients. In ITU-T H.265, the degree of quantization may be determined by a quantization parameter, QP. In ITU-T H.265, for a bit-depth of 8-bits, the QP can take 52 values from 0 to 51 and a change of 1 for QP generally corresponds to a change in the value of the quantization scaling factor by approximately 12%. It should be noted that more generally, in ITU-T H.265, the valid range of QP values for a source bit-depth is: −6*(bitdepth−8) to +51 (inclusive). Thus, for example, in the case where the bit-depth is 10-bits, QP can take 64 values from −12 to 51, which may be mapped to values 0 to 63 during dequantization. In ITU-T H.265, a quantization parameter may be updated for each CU and a respective quantization parameter may be derived for each of luma and chroma components. It should be noted that as the degree of quantization increases (e.g., transform coefficients are divided by a larger scaling factor value), the amount of distortion may be increased (e.g., reconstructed video data may appear more “blocky” to a user).

In some cases, blocking artifacts may cause coding block boundaries of reconstructed video data to be visually perceptible to a user. In order to reduce blocking artifacts, reconstructed sample values may be modified to minimize artifacts introduced by the video coding process. Such modifications may generally be referred to as filtering. It should be noted that filtering may occur as part of an in-loop filtering process or a post-loop filtering process. For an in-loop filtering process, the resulting sample values of a filtering process may be used for predictive video blocks (e.g., stored to a reference frame buffer for subsequent encoding at a video encoder and subsequent decoding at a video decoder). For a post-loop filtering process the resulting sample values of a filtering process are merely output as part of the decoding process (e.g., not used for subsequent coding). For example, for an in-loop filtering process, the sample values resulting from filtering a reconstructed block would be used for subsequent decoding (e.g., stored to a reference buffer) and would be output (e.g., to a display). For a post-loop filtering process, the reconstructed block without modification would be used for subsequent decoding and the sample values resulting from filtering the reconstructed block would be output.

With respect to the equations used herein, the following arithmetic operators may be used:

$\begin{matrix}  + & {Addition} \\  - & {Subtraction} \\ * & {{Multiplication},{{including}\mspace{14mu}{matrix}\mspace{14mu}{multiplication}}} \\ / & {{{Integer}\mspace{14mu}{division}\mspace{14mu}{with}\mspace{14mu}{truncation}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{result}\mspace{14mu}{toward}}\mspace{14mu}} \\ \; & {{{{zero}.\mspace{14mu}{For}}\mspace{14mu}{example}},{{{7/4}\mspace{14mu}{and}}\mspace{14mu} - {{7/{- 4}}\mspace{14mu}{are}\mspace{14mu}{truncated}\mspace{14mu}{to}\mspace{14mu} 1}}} \\ \; & {{and}\mspace{14mu} - {{7/4}\mspace{14mu}{and}\mspace{14mu}{7/{- 4}}\mspace{14mu}{are}\mspace{14mu}{truncated}\mspace{14mu}{to}}\mspace{14mu} - 1.} \\ {\sum\limits_{i = x}^{y}{f(i)}} & {{The}\mspace{14mu}{summation}\mspace{14mu}{of}\mspace{14mu}{f(i)}\mspace{14mu}{with}\mspace{14mu} i\mspace{14mu}{taking}\mspace{14mu}{all}\mspace{14mu}{integer}\mspace{14mu}{values}} \\ \; & {{from}\mspace{14mu} x\mspace{14mu}{up}\mspace{14mu}{to}\mspace{14mu}{and}\mspace{14mu}{including}\mspace{14mu}{y.}} \end{matrix}$

Further, the following mathematical functions may be used:

${{Clip}\; 3\left( {x,y,z} \right)} = \left\{ \begin{matrix} {x;} & {z < x} \\ {y;} & {z > y} \\ {z;} & {otherwise} \end{matrix} \right.$

-   -   Clip1c(x)=Clip3(0, (1<<BitDepth_(C))−1, x), where is         BitDepth_(C) bitdepth of chroma channel     -   abs(x) is the absolute value of x.

${{Max}\left( {x,y} \right)} = \left\{ \begin{matrix} {x;} & {x>=y} \\ {y;} & {x < y} \end{matrix} \right.$

Further, the following definitions of logical operators may be applied:

-   -   x && y Boolean logical “and” of x and y     -   x∥y Boolean logical “or” of x and y     -   ! Boolean logical “not”     -   x?y:z If x is TRUE or not equal to 0, evaluates to the value of         y; otherwise, evaluates to the value of z.

Further, the following relational operators may be applied:

-   -   > Greater than     -   >= Greater than or equal to     -   < Less than     -   <= Less than or equal to     -   == Equal to     -   != Not equal to

Further, the following bit-wise operators may be applied:

-   -   x>>y Arithmetic right shift of a two's complement integer         representation of x by y binary digits. This function is defined         only for non-negative integer values of y. Bits shifted into the         most significant bits (MSBs) as a result of the right shift have         a value equal to the MSB of x prior to the shift operation.     -   x<<y Arithmetic left shift of a two's complement integer         representation of x by y binary digits. This function is defined         only for non-negative integer values of y. Bits shifted into the         least significant bits (LSBs) as a result of the left shift have         a value equal to 0.

Deblocking (or de-blocking), deblock filtering, performing deblocking, or applying a deblocking filter refers to the process of smoothing video block boundaries with neighboring reconstructed video blocks (i.e., making boundaries less perceptible to a viewer). Smoothing the boundaries of neighboring reconstructed video blocks may include modifying sample values included in rows or columns adjacent to a boundary. ITU-T H.265 provides where a deblocking filter is applied to reconstructed sample values as part of an in-loop filtering process. ITU-T H.265 includes two types deblocking filters that may be used for modifying luma samples: a Strong Filter which modifies sample values in the three adjacent rows or columns to a boundary and a Weak Filter which modifies sample values in the immediately adjacent row or column to a boundary and conditionally modifies sample values in the second row or column from the boundary. Further, ITU-T H.265 includes one type of filter that may be used for modifying chroma samples, i.e., a Normal Filter.

FIGS. 5A-5B illustrate sample values included in video blocks P and Q having a boundary. As used herein, video blocks P and Q are used to refer to adjacent video blocks having a block boundary at which deblocking may be applied. The manner in which sample values are modified may be based on defined filters, where p_(i) and q_(i) represent respective sample values in a column for a vertical boundary and sample values in a row for a horizontal boundary and p_(i)′ and q_(i)′ represent modified sample values. Defined filters may define samples that are to be modified (or filtered) and samples that are used to determine how samples are to be modified. For example, as illustrated in FIG. 5A, in one example, samples values in each of the first three columns adjacent to the deblocking boundary may be modified (illustrated as filtered samples) based on sample values includes in the each of the first four columns adjacent to the deblocking boundary (illustrated as support samples).

As described above, ITU-T H.265 includes two types of filters that may be used for modifying luma samples: a Strong Filter and a Weak Filter. Simplified definitions of the Strong Filter and Weak Filter equations for modifying luma sample values are provided below. The definitions are simplified in that they do not include clipping operations provided in ITU-T H.265 (i.e., in ITU-T H.265, filtered values are clipped based on a value t_(C), described below), however, reference is made to Section 8.7.2.5.7 of ITU-T H.265, which provides the complete definitions.

Strong Filter p ₀′=(p ₂+2*p ₁+2*p ₀+2*q ₀ +q ₁+4)/8 p ₁′=(p ₂ +p ₁ +p ₀ +q ₀+2)/4 p ₂′=(2*p ₃+3*p ₂ +p ₁ +p ₀ +q ₀+4)/8 q ₀′=(p ₁+2*p ₀+2*q ₀+2*q ₁ +q ₂+4)/8 q ₁′=(p ₀ +q ₀ +q ₁ +q ₂+2)/4 q ₂′=(p ₀ +q ₀ +q ₁+3*q ₂+2*q ₃+4)/8

Weak Filter Δ=(9*(q ₀ −p ₀)−3*(q ₁ −p ₁)+8)/16 p ₀ ′=p ₀+Δ q ₀ ′=q ₀−Δ

-   -   Where p₁ and q₁ are conditionally modified, as described below,         as follows         Δp=((p ₂ +p ₀+1)/2−p ₁+Δ)/2         Δq=((q ₂ +p ₀+1)/2−q ₁−Δ)/2         p ₁ ′=p ₁ +Δp         q ₁ ′=q ₁ +Δq

Further, ITU-T H.265 includes one type of filter that may be used for modifying chroma samples: Normal Filter. Simplified definitions for the Normal Filter equations for modifying chroma sample values are provided below.

Normal Filter Δ=((q ₀ −p ₀)*4+p ₁ −q ₁+4)/8 p ₀ ′=p ₀+Δ q ₀ ′=q ₀−Δ

Deblocking may be performed based on a deblocking granularity. ITU-T H.265 provides an 8×8 deblocking granularity. That is, in ITU-T H.265 for an area of a picture, each edge lying on the 8×8 grid is evaluated to determine if a boundary exists. Further, in ITU-T H.265, a boundary strength (Bs) is determined for each boundary. In ITU-T H.265, Bs is determined as one of 0, 1, or 2 as follows:

-   -   P and Q are two adjacent coding blocks then the filter strength         Bs is specified as:         -   If one of the blocks (P or Q) has an intra prediction mode,             then Bs=2;             -   Else if P and Q belong to different TBs and P or Q has                 at least one non-zero             -   transform coefficient, then Bs=1;             -   Else if the reference pictures of P and Q are not equal,                 then Bs=1;             -   Else if the difference between x or y motion vector                 component of P and     -   Q is equal or greater than one integer sample, then Bs=1;         -   Else, Bs=0.

In ITU-T H.265, based on the QP used for coding the CBs including video blocks P and Q (which may be referred to as QP_(P) and QP_(Q)), variables t_(C)′ and β′ are determined. FIG. 6A provides a table for determining t_(C)′ and β′. In ITU-T H.265, the index Q is determined as follows:

For Luma:

-   -   For β′;         Q=Clip3(0,51,qP _(L)+(slice_beta_offset_div2<<1))     -   For t_(c)′         Q=Clip3(0,53,qP _(L)+2*(bS−1)+(slice_tc_offset_div2<<1)),     -   where,         qP _(L)=(QP _(Q) +QP _(P)+1)/2;     -   slice_beta_offset_div2 is an offset value that applies to the         slice of video data that includes sample q_(0,0); and     -   slice_tc_offset_div2 is an offset value that applies to the         slice of video data that includes sample q_(0,0).

ITU-T H.265, variables β and t_(C) are derived as follows: β=β′*(1<<(BitDepth_(Y)−8)) t _(C) =t _(C)′*(1<<(BitDepth_(Y)−8))

-   -   where, BitDepth_(Y) specifies the bit depth of luma samples.

ITU-T H.265, defines a variable d, where d is determined based on luma sample values as follows: dp0=abs(p _(2,0)−2*p _(1,0) +p _(0,0)) dp3=abs(p _(2,3)−2*p _(1,3) +p _(0,3)) dq0=abs(q _(2,0)−2*q _(1,0) +q _(0,0)) dq3=abs(q _(2,3)−2*q _(1,3) +q _(0,3)) dpq0=dp0+dq0 dpq3=dp3+dq3 dp=dp0+dp3 dq=dq0+dq3 d=dpq0+dpq3

Further, in ITU-T H.265 a variable dpq is set to a value based on the values of d and β. Finally, in ITU-T H.265, each of Bs, t_(C), β, and d are used to determine which filter type to apply (e.g., Strong Filter or Weak Filter). Further, in ITU-T H.265, for the chroma component, the Normal Filter is applied only when Bs equals 2. That is, in ITU-T H.265, deblocking only occurs for the chroma component if one the blocks P or Q is generated using an intra prediction mode.

It should be noted, that it may be useful to generally describe a deblocking filter according to a set of filter parameters. For example, for a set of sample values {a . . . b} included in a row or column, a corresponding deblocked sample value, y[n] may be specified based on the following equation:

${y\lbrack n\rbrack} = {\sum\limits_{m = a}^{b}{{{coeff}\lbrack m\rbrack}{x\left\lbrack {n + m} \right\rbrack}}}$

-   -   Where,     -   A filter length is determined as abs(a−b+1);     -   coeff[m] provides a filter tap value (also referred to as a         filter coefficient). For example, for {a . . . b}={0 . . . 4}, a         set of tap values may be {1, 2, 3, 2, 1};     -   x[n+m] provides input sample values corresponding to support         samples, it should be noted that the support size may be greater         than or equal to the filter length.

Further, in ITU-T H.265, the deblocking filter may be applied differently to CTU boundaries that coincide with slice and tile boundaries compared with CTU boundaries that do not coincide with slice and tile boundaries. Specifically, ITU-T H.265 specifies a flag, slice_loop_filter_across_slices_enabled_flag, present in a slice segment header that enables/disables the deblocking filter across CTU boundaries that coincide with top and left slice boundaries. ITU-T H.265 provides the following definition for slice_loop_filter_across_slices_enabled_flag:

slice_loop_filter_across_slices_enabled_flag equal to 1 specifies that in-loop filtering operations may be performed across the left and upper boundaries of the current slice. slice_loop_filter_across_slices_enabled_flag equal to 0 specifies that in-loop operations are not performed across left and upper boundaries of the current slice. The in-loop filtering operations include the deblocking filter and sample adaptive offset filter. When slice_loop_filter_across_slices_enabled_flag is not present, it is inferred to be equal to pps_loop_filter_across_slices_enabled_flag. Where pps_loop_filter_across_slices_enabled_flag is present in a picture parameter set (PPS) and ITU-T H.265 provides the following definition for pps_loop_filter_across_slices_enabled_flag: pps_loop_filter_across_slices_enabled_flag equal to 1 specifies that in-loop filtering operations may be performed across left and upper boundaries of slices referring to the PPS. pps_loop_filter_across_slices_enabled_flag equal to 0 specifies that in-loop filtering operations are not performed across left and upper boundaries of slices referring to the PPS. The in-loop filtering operations include the deblocking filter and sample adaptive offset filter operations. NOTE—Loop filtering across slice boundaries can be enabled while loop filtering across tile boundaries is disabled and vice versa.

Similarly, a flag, loop_filter_across_tiles_enabled_flag, present in a PPS enables/disables the deblocking filter across CTU boundaries that coincide with tile boundaries. ITU-T H.265 provides the following definition for loop_filter_across_tiles_enabled_flag:

loop_filter_across_tiles_enabled_flag equal to 1 specifies that in-loop filtering operations may be performed across tile boundaries in pictures referring to the PPS. loop_filter_across_tiles_enabled_flag equal to 0 specifies that in-loop filtering operations are not performed across tile boundaries in pictures referring to the PPS. The in-loop filtering operations include the deblocking filter and sample adaptive offset filter operations. When not present, the value of loop_filter_across_tiles_enabled_flag is inferred to be equal to 1.

As described above, for deblocking, the index Q is determined based on slice_beta_offset_div2 and slice_tc_offset_div2. In ITU-T H.265, the values of slice_beta_offset_div2 and slice_tc_offset_div2 may be included in a slice segment header and have the following definitions:

slice_beta_offset_div2 and slice_tc_offset_div2 specify the deblocking parameter offsets for β and t_(C) (divided by 2) for the current slice. The values of slice_beta_offset_div2 and slice_tc_offset_div2 shall both be in the range of −6 to 6, inclusive. When not present, the values of slice_beta_offset_div2 and slice_tc_offset_div2 are inferred to be equal topps_beta_offset_div2 and pps_tc_offset_div2, respectively. Where pps_beta_offset_div2 and pps_tc_offset_div2 are present in a PPS and ITU-T H.265 provides the following definition for pps_beta_offset_div2 and pps_tc_offset_div2: pps_beta_offset_div2 and pps_tc_offset_div2 specify the default deblocking parameter offsets for β and t_(C) (divided by 2) that are applied for slices referring to the PPS, unless the default deblocking parameter offsets are overridden by the deblocking parameter offsets present in the slice headers of the slices referring to the PPS. The values of pps_beta_offset_div2 and pps_tc_offset_div2 shall both be in the range of −6 to 6, inclusive. When not present, the value of pps_beta_offset_div2 and pps_tc_offset_div2 are inferred to be equal to 0.

As described above, ITU-T H.265 provides an 8×8 deblocking granularity. In JEM, deblocking is performed according to a grid specified by a variable minCUWidth for a horizontal boundary or a variable minCUHeight for a vertical boundary, where the default values of minCUWidth and minCUHeight are 4. A value of d is also determined in JEM where the calculation of d is same with that in ITU-T H.265. Based on the value of d above, a determination is made whether to perform deblocking on the boundary. That is, if d<β, a deblocking filter is used for the current boundary other, no deblocking is performed on the boundary. Further, in JEM a determination to use a strong or a weak filter is identical that in ITU-T H.265. Finally, in the JEM reference software, the luma filter coefficients for the strong deblocking filters is identical with the coefficients used in ITU-T H.265. Deblocking as performed in ITU-T H.265 and JEM may be less than ideal. In particular deblocking as perform in ITU-T H.265 and JEM fail to consider various coding parameters and properties of reconstructed video data when performing deblocking.

FIG. 7 is a block diagram illustrating an example of a system that may be configured to code (i.e., encode and/or decode) video data according to one or more techniques of this disclosure. System 100 represents an example of a system that may encapsulate video data according to one or more techniques of this disclosure. As illustrated in FIG. 7 , system 100 includes source device 102, communications medium 110, and destination device 120. In the example illustrated in FIG. 7 , source device 102 may include any device configured to encode video data and transmit encoded video data to communications medium 110. Destination device 120 may include any device configured to receive encoded video data via communications medium 110 and to decode encoded video data. Source device 102 and/or destination device 120 may include computing devices equipped for wired and/or wireless communications and may include, for example, set top boxes, digital video recorders, televisions, desktop, laptop or tablet computers, gaming consoles, medical imagining devices, and mobile devices, including, for example, smartphones, cellular telephones, personal gaming devices.

Communications medium 110 may include any combination of wireless and wired communication media, and/or storage devices. Communications medium 110 may include coaxial cables, fiber optic cables, twisted pair cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. Communications medium 110 may include one or more networks. For example, communications medium 110 may include a network configured to enable access to the World Wide Web, for example, the Internet. A network may operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include Digital Video Broadcasting (DVB) standards, Advanced Television Systems Committee (ATSC) standards, Integrated Services Digital Broadcasting (ISDB) standards, Data Over Cable Service Interface Specification (DOCSIS) standards, Global System Mobile Communications (GSM) standards, code division multiple access (CDMA) standards, 3rd Generation Partnership Project (3GPP) standards, European Telecommunications Standards Institute (ETSI) standards, Internet Protocol (IP) standards, Wireless Application Protocol (WAP) standards, and Institute of Electrical and Electronics Engineers (IEEE) standards.

Storage devices may include any type of device or storage medium capable of storing data. A storage medium may include a tangible or non-transitory computer-readable media. A computer readable medium may include optical discs, flash memory, magnetic memory, or any other suitable digital storage media. In some examples, a memory device or portions thereof may be described as non-volatile memory and in other examples portions of memory devices may be described as volatile memory. Examples of volatile memories may include random access memories (RAM), dynamic random access memories (DRAM), and static random access memories (SRAM). Examples of non-volatile memories may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. Storage device(s) may include memory cards (e.g., a Secure Digital (SD) memory card), internal/external hard disk drives, and/or internal/external solid state drives. Data may be stored on a storage device according to a defined file format.

Referring again to FIG. 7 , source device 102 includes video source 104, video encoder 106, data encapsulator 107, and interface 108. Video source 104 may include any device configured to capture and/or store video data. For example, video source 104 may include a video camera and a storage device operably coupled thereto. Video encoder 106 may include any device configured to receive video data and generate a compliant bitstream representing the video data. A compliant bitstream may refer to a bitstream that a video decoder can receive and reproduce video data therefrom. Aspects of a compliant bitstream may be defined according to a video coding standard. When generating a compliant bitstream video encoder 106 may compress video data. Compression may be lossy (discernible or indiscernible to a viewer) or lossless.

FIG. 8 is a block diagram illustrating an example of video encoder 200 that may implement the techniques for encoding video data described herein. It should be noted that although example video encoder 200 is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video encoder 200 and/or sub-components thereof to a particular hardware or software architecture. Functions of video encoder 200 may be realized using any combination of hardware, firmware, and/or software implementations. In one example, video encoder 200 may be configured to encode video data according to the techniques described herein. Video encoder 200 may perform intra prediction coding and inter prediction coding of picture areas, and, as such, may be referred to as a hybrid video encoder. In the example illustrated in FIG. 8 , video encoder 200 receives source video blocks. In some examples, source video blocks may include areas of picture that has been divided according to a coding structure. For example, source video data may include macroblocks, CTUs, CBs, sub-divisions thereof, and/or another equivalent coding unit. In some examples, video encoder may be configured to perform additional sub-divisions of source video blocks. It should be noted that the techniques described herein are generally applicable to video coding, regardless of how source video data is partitioned prior to and/or during encoding. In the example illustrated in FIG. 9 , video encoder 200 includes summer 202, transform coefficient generator 204, coefficient quantization unit 206, inverse quantization/transform processing unit 208, summer 210, intra prediction processing unit 212, inter prediction processing unit 214, filter unit 216, and entropy encoding unit 218. As illustrated in FIG. 8 , video encoder 200 receives source video blocks and outputs a bitstream.

In the example illustrated in FIG. 8 , video encoder 200 may generate residual data by subtracting a predictive video block from a source video block. Summer 202 represents a component configured to perform this subtraction operation. In one example, the subtraction of video blocks occurs in the pixel domain. Transform coefficient generator 204 applies a transform, such as a discrete cosine transform (DCT), a discrete sine transform (DST), or a conceptually similar transform, to the residual block or sub-divisions thereof (e.g., four 8×8 transforms may be applied to a 16×16 array of residual values) to produce a set of residual transform coefficients. Transform coefficient generator 204 may be configured to perform any and all combinations of the transforms included in the family of discrete trigonometric transforms. Transform coefficient generator 204 may output transform coefficients to coefficient quantization unit 206.

Coefficient quantization unit 206 may be configured to perform quantization of the transform coefficients. As described above, the degree of quantization may be modified by adjusting a quantization scaling factor which may be determined by quantization parameters. Coefficient quantization unit 206 may be further configured to determine quantization values and output QP data that may be used by a video decoder to reconstruct a quantization parameter to perform inverse quantization during video decoding. For example, signaled QP data may include QP delta values. In ITU-T H.265, the degree of quantization applied to a set of transform coefficients may depend on slice level parameters, parameters inherited from a previous coding unit, and/or optionally signaled CU level delta values.

As illustrated in FIG. 8 , quantized transform coefficients are output to inverse quantization/transform processing unit 208. Inverse quantization/transform processing unit 208 may be configured to apply an inverse quantization and/or an inverse transformation to generate reconstructed residual data. As illustrated in FIG. 8 , at summer 210, reconstructed residual data may be added to a predictive video block. In this manner, an encoded video block may be reconstructed and the resulting reconstructed video block may be used to evaluate the encoding quality for a given quality for a given prediction, transformation type, and/or level of quantization. Video encoder 200 may be configured to perform multiple coding passes (e.g., perform encoding while varying one or more coding parameters). The rate-distortion of a bitstream or other system parameters may be optimized based on evaluation of reconstructed video blocks. Further, reconstructed video blocks may be stored and used as reference for predicting subsequent blocks.

As described above, a video block may be coded using an intra prediction. Intra prediction processing unit 212 may be configured to select an intra prediction mode for a video block to be coded. Intra prediction processing unit 212 may be configured to evaluate a frame and/or an area thereof and determine an intra prediction mode to use to encode a current block. As illustrated in FIG. 8 , intra prediction processing unit 212 outputs intra prediction data (e.g., syntax elements) to filter unit 216 and entropy encoding unit 218.

Inter prediction processing unit 214 may be configured to perform inter prediction coding for a current video block. Inter prediction processing unit 214 may be configured to receive source video blocks and calculate a motion vector for PUs, or the like, of a video block. A motion vector may indicate the displacement of a PU, or the like, of a video block within a current video frame relative to a predictive block within a reference frame. Inter prediction coding may use one or more reference pictures. Further, motion prediction may be uni-predictive (use one motion vector) or bi-predictive (use two motion vectors). Inter prediction processing unit 214 may be configured to select a predictive block by calculating a pixel difference determined by, for example, sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. A motion vector and associated data may describe, for example, a horizontal component of the motion vector, a vertical component of the motion vector, a resolution for the motion vector (e.g., one-quarter pixel precision), a prediction direction and/or a reference picture index value. Further, a coding standard, such as, for example ITU-T H.265, may support motion vector prediction. Motion vector prediction enables a motion vector to be specified using motion vectors of neighboring blocks. Examples of motion vector prediction include advanced motion vector prediction (AMVP), temporal motion vector prediction (TMVP), so-called “merge” mode, and “skip” and “direct” motion inference. Inter prediction processing unit 214 may be configured to perform motion vector prediction according to one or more of the techniques described above. Inter prediction processing unit 214 may be configured to generate a predictive block using the motion prediction data. For example, inter prediction processing unit 214 may locate a predictive video block within a frame buffer (not shown in FIG. 8 ). It should be noted that inter prediction processing unit 214 may further be configured to apply one or more interpolation filters to a reconstructed residual block to calculate sub-integer pixel values for use in motion estimation. Inter prediction processing unit 214 may output motion prediction data for a calculated motion vector to filter unit 216 and entropy encoding unit 218.

As described above, deblocking refers to the process of smoothing the boundaries of reconstructed video blocks. As illustrated in FIG. 8 , filter unit 216 receives reconstructed video blocks and coding parameters (e.g., intra prediction data, inter prediction data, and QP data) and outputs modified reconstructed video data. Filter unit 216 may be configured to perform deblocking and/or Sample Adaptive Offset (SAO) filtering. SAO filtering is a non-linear amplitude mapping that may be used to improve reconstruction by adding an offset to reconstructed video data. It should be noted that as illustrated in FIG. 8 , intra prediction processing unit 212 and inter prediction processing unit 214 may receive modified reconstructed video block via filter unit 216. That is, in some cases, deblocking may occur in-loop, i.e., predictive video blocks stored in a reference buffer may be filtered. In some cases, deblocking may occur post-loop, i.e., after video data has been reconstructed and prior to being output to a display, for example. The techniques described herein may be applicable in-loop deblocking, post-loop deblocking, and/or combinations thereof.

As described above, deblocking as performed in ITU-T H.265 and JEM may be less than ideal. In one example, according to the techniques herein, filter unit 216 may be configured to select different filtering lines (in some cases, the number of samples deblocked on each side of boundary may be different) based on one or more of: block size on each side of boundary (one or both), boundary strength, prediction mode used by blocks on each side of boundary, prediction mode (e.g. intra, inter, skip) of sample being deblocked (e.g., use weaker filter for boundary close to reference samples), QP value of sample being deblocked, block size corresponding to the sample being deblocked, block size corresponding to the samples being used for deblocking, motion vectors for blocks on each side of boundary being deblocked, motion vectors for sample being deblocked, and/or motion vectors for sample being used for deblocking.

Samples on each side of a block boundary (perpendicular to the boundary edge) may be represented as: . . . p ₈ p ₇ p ₆ p ₅ p ₄ p ₃ p ₂ p ₁ p ₀ |q ₀ q ₁ q ₂ q ₃ q ₄ q ₅ q ₆ q ₇ q ₈ . . .

-   -   Where,     -   | represents the block boundary edge.     -   The samples p_(x), where x is a positive integer starting at 0,         represents the P-side of the boundary.     -   The samples q_(y) where y is a positive integer starting at 0,         represents the Q-side of the boundary.

In an example, P-side represents samples outside the current CU, Q-side represents samples inside the current CU.

In an example, P-side represents samples inside the current CU, Q-side represents samples outside the current CU.

In an example, P-side represents samples outside the current block, Q-side represents samples inside the current block.

In an example, P-side represents samples inside the current block, Q-side represents samples outside the current block.

Referring FIG. 5A, samples p_(y,x) and q_(y,x) correspond to line R[x] when deblocking vertical edge.

Referring FIG. 5B, samples p_(y,x) and q_(y,x) correspond to line R[y] when deblocking horizontal edge.

One example of a wider (i.e. larger number of samples deblocked), stronger filter for P-side of the boundary, referred to as WS00P P-side filter, is: p ₆′=(7*p ₇+2*p ₆ +p ₅ +p ₄ +p ₃ +p ₂ +p ₁ +p ₀ +q ₀+8)>>4 p ₅′=(6*p ₇ +p ₆+2*p ₅ +p ₄ +p ₃ +p ₂ +p ₁ +p ₀ +q ₀ +q ₁+8)>>4 p ₄′=(5*p ₇ +p ₆ +p ₅+2*p ₄ +p ₃ +p ₂ +p ₁ +p ₀ +q ₀ +q ₁ +q ₂+8)>>4 p ₃′=(4*p ₇ +p ₆ +p ₅ +p ₄+2*p ₃ +p ₂ +p ₁ +p ₀ +q ₀ +q ₁ +q ₂ +q ₃++8)>>4 p ₂′=(3*p ₇ +p ₆ +p ₅ +p ₄ +p ₃+2*p ₂ +p ₁ +p ₀ +q ₀ +q ₁ +q ₂ +q ₃ +q ₄+8)>>4 p ₁′=(2*p ₇ +p ₆ +p ₅ +p ₄ +p ₃ +p ₂+2*p ₁ +p ₀ +q ₀ +q ₁ +q ₂ +q ₃ +q ₄ +q ₅+8)>>4 p ₀′=(p ₇ +p ₆ +p ₅ +p ₄ +p ₃ +p ₂ +p ₁+2*p ₀ +q ₀ +q ₁ +q ₂ +q ₃ +q ₄ +q ₅ +q ₆+8)>>4

-   -   where, p_(x)′ represents the sample value after deblocking at         position corresponding to p_(x)

One example of a wider (i.e. larger number of samples deblocked), stronger filter for Q-side of the boundary, referred to as WS00Q Q-side filter, is: q ₆′=(7*q ₇+2*q ₆ +q ₅ +q ₄ +q ₃ +q ₂ +q ₁ +q ₀ +p ₀+8)>>4 q ₅′=(6*q ₇ +q ₆+2*q ₅ +q ₄ +q ₃ +q ₂ +q ₁ +q ₀ +p ₀ +p ₁+8)>>4 q ₄′=(5*q ₇ +q ₆ +q ₅+2*q ₄ +q ₃ +q ₂ +q ₁ +q ₀ +p ₀ +p ₁ +p ₂+8)>>4 q ₃′=(4*q ₇ +q ₆ +q ₅ +q ₄+2*q ₃ +q ₂ +q ₁ +q ₀ +p ₀ +p ₁ +p ₂ +p ₃+8)>>4 q ₂′=(3*q ₇ +q ₆ +q ₅ +q ₄ +q ₃+2*q ₂ +q ₁ +q ₀ +p ₀ +p ₁ +p ₂ +p ₃ +p ₄+8)>>4 q ₁′=(2*q ₇ +q ₆ +q ₅ +q ₄ +q ₃ +q ₂+2*q ₁ +q ₀ +p ₀ +p ₁ +p ₂ +p ₃ +p ₄ +p ₅+8)>>4 q ₀′=(q ₇ +q ₆ +q ₅ +q ₄ +q ₃ +q ₂ +q ₁+2*q ₀ +p ₀ +p ₁ +p ₂ +p ₃ +p ₄ +p ₅ +p ₆+8)>>4

-   -   where, q_(x)′ represents the sample value after deblocking at         position corresponding to q_(x)

One example of a narrow (i.e. smaller number of samples deblocked), strong filter for P-side of the boundary, referred to as HEVC_P P-side filter, is: p ₀′=(p ₂+2*p ₁+2*p ₀+2*q ₀ +q ₁+4)>>3 p ₁′=(p ₂ +p ₁ +p ₀ +q ₀+2)>>2 p ₂′=(2*p ₃+3*p ₂ +p ₁ +p ₀ +q ₀+4)>>3

-   -   where, p_(x)′ represents the sample value after deblocking at         position corresponding to p_(x)

One example of a narrow (i.e. smaller number of samples deblocked), strong filter for Q-side of the boundary, referred to as HEVC_Q Q-side filter, is: q ₀′=(p ₁+2*p ₀+2*q ₀+2*q ₁ +q ₂+4)>>3 q ₁′=(p ₀ +q ₀ +q ₁ +q ₂+2)>>2 q ₂′=(p ₀ +q ₀ +q ₁+3*q ₂+2*q ₃+4)>>3

-   -   where, q_(x)′ represents the sample value after deblocking at         position corresponding to q_(x)

One example of a narrow (smaller number of samples deblocked), strong filter for P-side of the boundary, referred to as NS00P P-side filter, is: p ₀′=(p ₂+2*p ₁+2*p ₀+2*q ₀ +q ₁+4)>>3 p ₁′=(p ₂ +p ₁ +p ₀ +q ₀+4)>>3 p ₂′=(p ₄+2*p ₃+3*p ₂ +p ₁ +p ₀+4)>>3

-   -   where, p_(x)′ represents the sample value after deblocking at         position corresponding to p_(x)

One example of a narrow (smaller number of samples deblocked), strong filter for Q-side of the boundary, referred to as NS00Q Q-side filter, is: q ₀′=(q ₂+2*q ₁+2*q ₀+2*p ₀ +p ₁+4)>>3 q ₁′=(q ₂ +q ₁ +q ₀ +p ₀+4)>>3 q ₂′=(q ₄+2*q ₃+3*q ₂ +q ₁ +q ₀+4)>>3

-   -   where, q_(x)′ represents the sample value after deblocking at         position corresponding to q_(x)

One example of a narrow (smaller number of samples deblocked), strong filter for P-side of the boundary, referred to as NS00P P-side filter, is: p ₀′=(p ₂+2*p ₁+2*p ₀+2*q ₀ +q ₁+4)>>3 p ₁′=(p ₂ +p ₁ +p ₀ +q ₀+2)>>2 p ₂′=(p ₄+2*p ₃+3*p ₂ +p ₁ +p ₀+4)>>3

One example of a narrow (smaller number of samples deblocked), strong filter for Q-side of the boundary, referred to as NS00Q Q-side filter, is: q ₀′=(q ₂+2*q ₁+2*q ₀+2*p ₀ +p ₁+4)>>3 q ₁′=(q ₂ +q ₁ +q ₀ +p ₀+2)>>2 q ₂′=(q ₄+2*q ₃+3*q ₂ +q ₁ +q ₀+4)>>3

One example of a narrow (smaller number of samples deblocked), strong filter for P-side of the boundary, referred to as NS00P P-side filter, is: p ₀′=(p ₂+2*p ₁+2*p ₀+2*q ₀ +q ₁+4)>>3 p ₁′=(p ₂ +p ₁ +p ₀ +q ₀+2)>>2 p ₂′=(2*p ₃+3*p ₂ +p ₁ +p ₀ +q ₀+4)>>3

One example of a narrow (smaller number of samples deblocked), strong filter for Q-side of the boundary, referred to as NS00Q Q-side filter, is: q ₀′=(q ₂+2*q ₁+2*q ₀+2*p ₀ +p ₁+4)>>3 q ₁′=(q ₂ +q ₁ +q ₀ +p ₀+2)>>2 q ₂′=(2*q ₃+3*q ₂ +q ₁ +q ₀ +p ₀+4)>>3

One example of a narrow (smaller number of samples deblocked), weak filter for P-side of the boundary, referred to as NW00P P-side filter, is: Δ=Clip3(−t _(C) ,t _(C),((((q ₀ −p ₀)<<2)+p ₁ −q ₁+4)>>3)) p ₀′=Clip1_(C)(p ₀+Δ)

-   -   where, p_(x)′ represents the sample value after deblocking at         position corresponding to p_(x)

One example of a narrow (smaller number of samples deblocked), weak filter for Q-side of the boundary, referred to as NW00Q Q-side filter, is: Δ=Clip3(−t _(C) ,t _(C),((((q ₀ −p ₀)<<2)+p ₁ −q ₁+4)>>3)) q ₀′=Clip1_(C)(q ₀−Δ)

-   -   where, q_(x)′ represents the sample value after deblocking at         position corresponding to q_(x)

One example of a filter for P-side of the boundary, referred to as FOP P-side filter, is: p ₀′=(136*p ₈+120*q ₈+128)>>8 p ₁′=(151*p ₇+105*q ₉+128)>>8 p ₂′=(166*p ₆+90*q ₁₀+128)>>8 p ₃′=(181*p ₅+75*q ₁₁+128)>>8 p ₄′=(196*p ₄+60*q ₁₂+128)>>8 p ₅′=(211*p ₃+45*q ₁₃+128)>>8 p ₆′=(226*p ₂+30*q ₁₄+128)>>8 p ₇′=(241*p ₁+15*q ₁₅+128)>>8

One example of a filter for Q-side of the boundary, referred to as F0Q Q-side filter, is: q ₀′=(120*p ₀+136*q ₇+128)>>8 q ₁′=(105*p ₁₀+151*q ₆+128)>>8 q ₂′=(90*p ₁₁+166*q ₅+128)>>8 q ₃′=(75*p ₁₂+181*q ₄+128)>>8 q ₄′=(60*p ₁₃+196*q ₃+128)>>8 q ₅′=(45*p ₁₄+211*q ₂+128)>>8 q ₆′=(30*p ₁₅+226*q ₁+128)>>8 q ₇′=(15*p ₁₆+241*q ₀+128)>>8

One example of a filter for P-side of the boundary, referred to as F1P P-side filter, is: p ₀′=(2*p ₁+4*p ₀ +q ₀ +q ₁+4)>>3 p ₁′=(2*p ₂+4*p ₁ +p ₀ +q ₀+4)>>3 p ₂′=(p ₃ +p ₂ +p ₁ +p ₀+²)>>2 p ₃′=(p ₄ +p ₃ +p ₂ +p ₁+2)>>2

One example of a filter for Q-side of the boundary, referred to as F1Q Q-side filter, is: q ₀′=(2*q ₁+4*q ₀ +p ₀ +p ₁+4)>>3 q ₁′=(2*q ₂+4*q ₁ +q ₀ +p ₀+4)>>3 q ₂′=(q ₃ +q ₂ +q ₁ +q ₀+2)>>2 q ₃′=(q ₄ +q ₃ +q ₂ +q ₁+2)>>2

In one example, the distance of a sample being deblocked from the boundary may be inversely proportional to the distance between the support sample assigned the largest tap value and the sample being deblocked. Further, the distance of a second largest tap value from a sample being deblocked may be proportional to the distance of the sample from the boundary. Filters F2P and F2Q described below provide example implementations of such a filtering. One example of a filter for P-side of the boundary, referred to as F2P P-side filter, is: p ₀′=(136*p ₈+2*p ₀+120*q ₈+256)>>9 p ₁′=(151*p ₇+4*p ₁+105*q ₉+256)>>9 p ₂′=(166*p ₆+8*p ₂+90′*q ₁₀+256)>>9 p ₃′=(181*p ₅+16*p ₃+75*q ₁₁+256)>>9 p ₄′=(196*p ₄+32*p ₄+60*q ₁₂+256)>>9 p ₅′=(211*p ₃+64*p ₅+45*q ₁₃+256)>>9 p ₆′=(226*p ₂+128*p ₆+30*q ₁₄+256)>>9 p ₇′=(241*p ₁+256*p ₇+15*q ₁₅+256)>>9

One example of a filter for Q-side of the boundary, referred to as F2Q Q-side filter, is: q ₀′=(120*p ₉+2*q ₀+136*q ₇+256)>>9 q ₁′=(105*p ₁₀+4*q ₁+151*q ₆+256)>>9 q ₂′=(90*p ₁₁+8*q ₂+166*q ₅+256)>>9 q ₃′=(75*p ₁₂+16*q ₃+181*q ₄+256)>>9 q ₄′=(60*p ₁₃+32*q ₄+196*q ₃+256)>>9 q ₅′=(45*p ₁₄+64*q ₅+211*q ₂+256)>>9 q ₆′=(30*p ₁₅+128*q ₆+226*q ₁+256)>>9 q ₇′=(15*p ₁₆+256*q ₇+241*q ₀+256)>>9

One example of a filter for P-side of the boundary, referred to as F4P P-side filter, is: p ₆′=(7*p ₇+2*p ₆ +p ₅ +p ₄ +p ₃ +p ₂ +p ₁ +p ₀ +q ₀+8)>>4 p ₅′=(6*p ₇ +p ₆+2*p ₅ +p ₄ +p ₃ +p ₂ +p ₁ +p ₀ +q ₀ +q ₁+8)>>4 p ₄′=(5*p ₇ +p ₆ +p ₅+2*p ₄ +p ₃ +p ₂ +p ₁ +p ₀ +q ₀ +q ₁ +q ₂+8)>>4 p ₃′=(4*p ₇ +p ₆ +p ₅ +p ₄+2*p ₃ +p ₂ +p ₁ +p ₀ +q ₀ +q ₁ +q ₂ +q ₃+8)>>4 p ₂′=(3*p ₇ +p ₆ +p ₅ +p ₄ +p ₃+2*p ₂ +p ₁ +p ₀ +q ₀ +q ₁ +q ₂ +q ₃ +q ₄+8)>>4 p ₁′=(2*p ₇ +p ₆ +p ₅ +p ₄ +p ₃ +p ₂+2*p ₁ +p ₀ +q ₀ +q ₁ +q ₂ +q ₃ +q ₄ +q ₅+8)>>4 p ₀′=(p ₇ +p ₆ +p ₅ +p ₄ +p ₃ +p ₂ +p ₁+2*p ₀ +q ₀ +q ₁ +q ₂ +q ₃ +q ₄ +q ₅ +q ₆+8)>>4

One example of a filter for Q-side of the boundary, referred to as F4Q Q-side filter, is: q ₆′=(7*q ₇+2*q ₆ +q ₅ +q ₄ +q ₃ +q ₂ +q ₁ +q ₀ +p ₀+8)>>4 q ₅′=(6*q ₇ +q ₆+2*q ₅ +q ₄ +q ₃ +q ₂ +q ₁ +q ₀ +p ₀ +p ₁+8)>>4 q ₄′=(5*q ₇ +q ₆ +q ₅+2*q ₄ +q ₃ +q ₂ +q ₁ +q ₀ +p ₀ +p ₁ +p ₂+8)>>4 q ₃′=(4*q ₇ +q ₆ +q ₅ +q ₄+2*q ₃ +q ₂ +q ₁ +q ₀ +p ₀ +p ₁ +p ₂ +p ₃+8)>>4 q ₂′=(3*q ₇ +q ₆ +q ₅ +q ₄ +q ₃+2*q ₂ +q ₁ +q ₀ +p ₀ +p ₁ +p ₂ +p ₃ +p ₄+8)>>4 q ₁′=(2*q ₇ +q ₆ +q ₅ +q ₄ +q ₃ +q ₂+2*q ₁ +q ₀ +p ₀ +p ₁ +p ₂ +p ₃ +p ₄ +p ₅+8)>>4 q ₀′=(q ₇ +q ₆ +q ₅ +q ₄ +q ₃ +q ₂ +q ₁+2*q ₀ +p ₀ +p ₁ +p ₂ +p ₃ +p ₄ +p ₅ +p ₆+8)>>4

One example of a filter for P-side of the boundary, referred to as CL_P-side filter, is: p ₂′=(3*p ₃+2*p ₂ +p ₁ +p ₀ +q ₀+4)>>3 p ₁′=(2*p ₃ +p ₂+2*p ₁ +p ₀ +q ₀ +q ₁+4)>>3 p ₀=(p ₃ +p ₂ +p ₁+2*p ₀ +q ₀ +q ₁ +q ₂+4)>>3

One example of a filter for Q-side of the boundary, referred to as CL_q Q-side filter, is: q ₂′=(3*q ₃+2*q ₂ +q ₁ +q ₀ +p ₀+4)>>3 q ₁′=(2*q ₃ +q ₂+2*q ₁ +q ₀ +p ₀ +p ₁+4)>>3 q ₀′=(q ₃ +q ₂ +q ₁+2*q ₀ +p ₀ +p ₁ +p ₂+4)>>3

In one example, according to the techniques herein, gradient computation may be used in selection of filter parameters, number of samples to be deblocked on one (or both) side of block boundary. Gradient may be computed using samples in line R[x].

In an example multiple gradients may be computed using samples in line R[x] and used in selection of filter parameters, number of samples to be deblocked on one (or both) side of block boundary. In another example, multiple gradients may be computed using samples in line R[x] and operations such as averaging of gradients, maximum gradient, minimum gradient, may be used in selection of filter parameters, number of samples to be deblocked on one (or both) side of block boundary.

In one example, function invocation xCalDQp(R[x]) computes gradient, as follows: abs(p ₂−2*p ₁ +p ₀)

In one example, function invocation xCalDQq(R[x]) computes gradient, as follows: abs(q ₂−2*q ₁ +q ₀)

In one example, function invocation xCalDQpLargeBlock(R[x]) computes gradient, as follows: Max(Max(Max(Max(Max(abs(p ₂−2*p ₁ +p ₀),abs(p ₃−2*p ₂ +p ₁)),abs(p ₄−2*p ₃ +p ₂)),abs(p ₅−2*p ₄ +p ₃)),abs(p ₆−2*p ₅ +p ₄)),abs(p ₇−2*p ₆ +p ₅))

In one example, function invocation xCalDQqLargeBlock(R[x]) computes gradient, as follows: Max(Max(Max(Max(Max(abs(q ₂−2*q ₁ +q ₀),abs(q ₃2*q ₂ +q ₁)),abs(q ₄−2*q ₃ +q ₂)),abs(q ₅−2*q ₄ +q ₃)),abs(q ₆−2*q ₅ +q ₄)),abs(q ₇−2*q ₆ +q ₅))

In one example, function invocation xCalDQpLargeBlock(R[x]) computes gradient, as follows: (abs(p ₂−2*p ₁ +p ₀)+abs(p ₃−2*p ₂ +p ₁)+abs(p ₅−2*p ₄ +p ₃)+abs(p ₇−2*p ₆ +p ₅)+4)>>2

In one example, function invocation xCalDQqLargeBlock(R[x]) computes gradient, as follows: (abs(q ₂−2*q ₁ +q ₀)+abs(q ₃−2*q ₂ +q ₁)+abs(q ₅−2*q ₄ +q ₅)+abs(q ₇−2*q ₆ +q ₅)+4)>>2

In one example, function invocation xCalDQpLargeBlock(R[x]) computes gradient, as follows: (abs(p ₂−2*p ₁ +p ₀)+abs(p ₃−2*p ₂ +p ₁)+abs(p ₅−2*p ₄ +p ₃)+abs(p ₇−2*p ₆ +p ₅)+2)>>2

In one example, function invocation xCalDQqLargeBlock(R[x]) computes gradient, as follows: (abs(q ₂−2*q ₁ +q ₀)+abs(q ₃−2*q ₂ +q ₁)+abs(q ₅−2*q ₄ +q ₃)+abs(q ₇−2*q ₄ +q ₅)+2)>>2

In one example, function invocation xCalDQpLargeBlock(R[x]) computes gradient, as follows: (abs(p ₂−2*p ₁ +p ₀)+abs(p ₃−2*p ₂ +p ₁)+abs(p ₄−2*p ₃ +p ₂)+abs(p ₅−2*p ₄ +p ₃)+4)>>2

In one example, function invocation xCalDQqLargeBlock(R[x]) computes gradient, as follows: (abs(q ₂−2*q ₁ +q ₀)+abs(q ₃−2*q ₂ +q ₁)+abs(q ₄−2*q ₃ +q ₂)+abs(q ₅−2*q ₄ +q ₃)+4)>>2

In one example, function invocation xCalDQpLargeBlock(R[x]) computes gradient, as follows: (abs(p ₂−2*p ₁ +p ₀)+abs(p ₃−2*p ₂ +m)+abs(p ₄−2*p ₃ +p ₂)+abs(p ₅−2*p ₄ +p ₃)+2)>>2

In one example, function invocation xCalDQqLargeBlock(R[x]) computes gradient, as follows: (abs(q ₂−2*q ₁ +q ₀)+abs(q ₃−2*q ₂ +q ₁)+abs(q ₄−2*q ₃ +q ₂)+abs(q ₅−2*q ₄ +q ₃)+2)>>2

In one example, function invocation xCalDQpLargeBlock(R[x]) computes gradient, as follows: (abs(p ₂−2*p ₁ +p ₀)+abs(p ₅−2*p ₄ +p ₃)+1)>>1

In one example, function invocation xCalDQqLargeBlock(R[x]) computes gradient, as follows: (abs(q ₂−2*q ₁ +q ₀)+abs(q ₅−2*q ₄ +q ₃)+1)>>1

In one example, a subset of second-order differences computed at p₁, p₂, . . . , p₆ may be used to compute xCalDQpLargeBlock(R[x]) where second order difference at p_(n) is abs(p_(n−1)−2*p_(n)+p_(n+1)). Similarly, a subset of second-order differences computed at q₁, q₂, . . . , q₆ may be used to compute xCalDQqLargeBlock(R[x]) In one example, the rounding offset in the function invocation xCalDQpLargeBlock(R[x]) and xCalDQqLargeBlock(R[x]) can be dropped.

In one example, function invocation xUseStrongFilteringLargeBlock (R[x], d, bSidePisLargeBlk, bSideQisLargeBlk) computes a Boolean variable, as follows, where examples for determined bSidePisLargeBlk, bSideQisLargeBlk are provided below: ((abs((bSidePisLargeBlk?p ₇ :p ₄)−p ₀)+abs((bSideQisLargeBlk?q ₇ :q ₄)−q ₀)<(β>>3))&&(d<(β>>2))&&(abs(q ₀ −p ₀)<((t _(C)*5+1)>>1)))?TRUE:FALSE, where β and t _(C) are thresholds.

In one example, function invocation xUseStrongFilteringLargeBlock (R[x], d, bSidePisLargeBlk, bSideQisLargeBlk) computes a Boolean variable, as follows:

sp₃ = Abs( p₃ − p₀ ) if (bSidePisLargeblk) { sp3 = max( sp3, max(Abs( p₇ − p₃ ), Abs( p₇ − p₀ )) } sq₃ = Abs( q₀ − q₃ ) if (bSideQisLargeblk) { sq₃ = max( sq₃, max(Abs( q₇ − q₃ ), Abs( q₇ − q₀ ))) } xUseStrongFilteringLargeBlock: sp₃ + sq₃ < (β>> 3) && (d < (β >> 2)) && (abs(q₀− p₀) < ((t_(C) * 5 + 1) >> 1)))? TRUE:FALSE.

In one example, function invocation xUseStrongFilteringLargeBlock (R[x], d, bSidePisLargeBlk, bSideQisLargeBlk) computes a Boolean variable, as follows:

sp₃ = Abs( p₃ − p₀ ) if (bSidePisLargeblk) { sp₃ = (sp₃ + Abs( p₇ − p₃ ) + 1)>>1 } sq₃ = Abs( q₀ − q₃ ) if (bSideQisLargeblk) { sq₃ = (sq₃ + Abs( q₇ − q₃ ) ) + 1)>>1 } xUseStrongFilteringLargeBlock: sp₃ + sq₃ < (β>> 3) && (d < (β >> 2)) && (abs(q₀− p₀) < ((t_(C) * 5 + 1) >> 1)))? TRUE:FALSE

In one example, function invocation xUseStrongFilteringLargeBlock (R[x], d, bSidePisLargeBlk, bSideQisLargeBlk) computes a Boolean variable, as follows:

sp₃ = Abs( p₃ − p₀ ) if (bSidePisLargeblk) { sp₃ = (sp₃ + Abs( p₇ − p₀ ) ) + 1)>>1 } sq₃ = Abs( q₀ − q₃ ) if (bSideQisLargeblk) { sq₃ = (sq₃ + Abs( q₇ − q₀ ) + 1)>>1 } xUseStrongFilteringLargeBlock: sp₃ + sq₃ < (β>> 3) && (d < (β >> 2)) && (abs(q₀− p₀) < ((t_(C) * 5 + 1) >> 1)))? TRUE:FALSE

In one example, the rounding offset in the function invocation xUseStrongFilteringLargeBlock can be dropped.

In one example, the condition used in selecting number of samples to be deblocked on one (or both) side of a boundary corresponds to the dimension (of current and/or neighboring block), perpendicular to block boundary, exceeding a threshold. In some cases, when a subset of transform coefficients is set to zero for a block, based on block size, then the threshold used in the comparison may be based on the properties of the subset of zero coefficients. For example, when transform coefficients is set to zero for coefficients in column position greater than or equal to 32 and row position greater than or equal to 32 (with row, column indexing starting at 0). then the dimension perpendicular to block boundary is compared to threshold value of 32.

In an example a signal may be received in the bitstream indicating whether all transform coefficients are zero for a block of samples. Such a signal may be received for e.g. for each color component, for a group of color components, for some spatial partitioning of samples, for some spatio-temporal partitioning of samples. In HEVC, for each color component a coded block flag (CBF) was signaled (either explicitly or implicitly by use of an inference rule in case of absence of explicit signal)—cbf_luma, cbf_cb, cbf_cr; moreover a flag was also signaled (explicitly and implicitly) indicating if any of the color components in the transform tree contained non-zero transform coefficients and was referred to as residual quad tree root CBF—rqt_root_cbf.

In one example the number of samples to be deblocked on one (or both) side of a boundary may be based on the type of edge being deblocked (e.g. vertical block edge, horizontal block edge). channel type (e.g. luma, chroma), whether all transform coefficients are zero for block of samples on one (or both) side of a boundary, whether block of samples on one (or both) side of boundary make use of coding modes such as Local Illumination Compensation (LIC) which may be based on a linear model for illumination changes, whether block of samples on one (or both) side of boundary make use of cross component prediction (which may be based on linear model), whether block of samples on one (or both) side of boundary make use prediction that is determined for blocks smaller than the transform, whether block of samples on one (or both) side of boundary make use techniques wherein large block (e.g. CU) is partitioned into sub-blocks (e.g. sub-CUs) and motion information is derived for these sub-blocks.

In one example, according to the techniques herein, a larger number of samples is (e.g. 7) is deblocked on each side of the block boundary when dimension of the current block, perpendicular to the block boundary, is greater than or equal to a threshold (e.g. 32) and a smaller number of samples (e.g. 3) is deblocked on each side of the block boundary when dimension of the current block, perpendicular to the block boundary, is smaller than a threshold (e.g. 32). For example, if ((width of current block>=32 and edge type is vertical) or (height of current block>=32 and edge type is horizontal)) deblock larger number of samples on each side of the block boundary.

In one example, according to the techniques herein, a larger number of samples is (e.g. 7) is deblocked on the side of the block boundary where dimension of the block, perpendicular to the block boundary, is greater than or equal to a threshold (e.g. 32) and a smaller number of samples (e.g. 3) is deblocked on side of the block boundary where dimension of the block, perpendicular to the block boundary, is smaller than a threshold (e.g. 32). For example: if ((width of one block>=32 and edge type is vertical) or (height of one block>=32 and edge type is horizontal)) deblock larger number of samples for that block at the block boundary. Here if the left-side of a vertical boundary edge has a block size 4 (rows)×64 (columns) and the right-side has a block size 4 (rows)×16 (columns) then larger number of samples may be deblocked on left-side versus the right side.

In one example, according to the techniques herein, filter unit 216 may be configured to select filter parameters (including, e.g., a number of coefficients) used for deblocking based on one or more of: distance of sample being deblocked (in number of samples) from boundary, block size(s) on each side of boundary, boundary strength, prediction mode used by blocks on each side of boundary, prediction mode of sample being deblocked (e.g., use weaker filter for boundary close to reference samples), QP of sample being deblocked (e.g., use stronger filters for larger QP), block size corresponding to the sample being deblocked (e.g., use stronger filters for larger block size), block size corresponding to the samples being used for deblocking, motion vectors for blocks on each side of boundary being deblocked (e.g., if the MV difference is larger than a threshold then do not perform any deblocking since samples on different side of the boundary may belong to different objects), and/or motion vectors for sample being deblocked; motion vectors for sample being used for deblocking. It should be noted that, block size corresponding to a sample may include the block size of CU the sample belongs to, block size of TU the sample belongs, to or the block size of PU the sample belongs to.

In one example, according to the techniques herein, filter unit 216 may be configured to select filter parameters (including, e.g., a number of coefficients) used for deblocking based on the type of edge being deblocked (e.g. vertical block edge, horizontal block edge), channel type (e.g. luma, chroma), whether all transform coefficients are zero for block of samples on one (or both) side of a boundary, whether block of samples on one (or both) side of boundary make use of coding modes such as Local Illumination Compensation (LIC) which may be based on a linear model for illumination changes, whether block of samples on one (or both) side of boundary make use of cross component prediction (which may be based on linear model), whether block of samples on one (or both) side of boundary make use prediction that is determined for blocks smaller than the transform, whether block of samples on one (or both) side of boundary make use techniques wherein large block (e.g. CU) is partitioned into sub-blocks (e.g. sub-CUs) and motion information is derived for these sub-blocks.

In one example, according to the techniques herein, filter unit 216 may be configured to select filter parameters (including, e.g., a number of coefficients) used for deblocking based on the type of edge being deblocked (e.g. vertical block edge, horizontal block edge), channel type (e.g. luma, chroma), whether all transform coefficients are zero for block of samples on one (or both) side of a boundary, whether block of samples on one (or both) side of boundary make use of coding modes such as Local Illumination Compensation (LIC) which may be based on a linear model for illumination changes, whether block of samples on one (or both) side of boundary make use of cross component prediction (which may be based on linear model), whether block of samples on one (or both) side of boundary make use prediction that is determined for blocks smaller than the transform, whether block of samples on one (or both) side of boundary make use techniques wherein large block (e.g. CU) is partitioned into sub-blocks (e.g. sub-CUs) and motion information is derived for these sub-blocks.

In one example selecting filter parameters may include selecting wider stronger filtering.

In one example, according to the techniques herein, filter unit 216 may be configured to select a set of deblocking filter parameters (e.g. wider stronger filtering) for both sides when dimension of the current block, perpendicular to the block boundary, is greater than or equal to a threshold (e.g. 32). For example, if ((width of current block>=32 and edge type is vertical) or (height of current block>=32 and edge type is horizontal)) then wider stronger filtering is selected for each side of the block boundary.

In one example, according to the techniques herein, filter unit 216 may be configured to select filter parameters for each side of block boundary independently based on dimension of the block, perpendicular to the block boundary, for the corresponding side. For example, when dimension of the block perpendicular to the block boundary on one side is greater than or equal to a threshold (e.g. 32) then a set of deblocking filter parameters (e.g. wider stronger filtering) may be selected for that side. For example: if ((width of one block>=32 and edge type is vertical) or (height of one block>=32 and edge type is horizontal)) wider stronger filtering is selected for the side of the block boundary corresponding to the block.

In one example, according to the techniques herein, sub-CU boundary may be deblocked based on whether all transform coefficients are zero for blocks (e.g. CU) on one (or both) side of a boundary. For example, deblock sub-CU boundary when all the transform coefficients for the CU is zero.

In one example, according to the techniques herein, sub-block boundary may be deblocked based on whether all transform coefficients are zero for a block on one (or both) side of a boundary. For example, deblock sub-block boundary when all the transform coefficients for the block is zero.

In one example, according to the techniques herein, sub-CU boundary may be deblocked based on whether all transform coefficients are zero for blocks (e.g. CU) on one (or both) side of a boundary and quantization step size is large (e.g QP greater than or equal to a threshold). For example, deblock sub-CU boundary when all the transform coefficients for the CU is zero and QP is greater than a threshold.

In one example, according to the techniques herein, sub-block boundary may be deblocked based on whether all transform coefficients are zero for a block on one (or both) side of a boundary and quantization step size is large (e.g QP greater than or equal to a threshold). For example, deblock sub-block boundary when all the transform coefficients for the block is zero and QP is greater than a threshold.

In one example, according to the techniques herein, a block boundary may be deblocked when Local Illumination Compensation (LIC) is used for blocks on one (or both) side of a boundary and all the transform coefficients for that block is zero.

In one example, according to the techniques herein, all four boundaries of a block (i.e. left, right, top, bottom) a block boundary may be deblocked when Local Illumination Compensation (LIC) is used for a block and all the transform coefficients for that block is zero.

In one example, according to the techniques herein, a block boundary may be deblocked when Local Illumination Compensation (LIC) is used for blocks on one (or both) side of a boundary and all the transform coefficients for that block is zero and quantization step size is large (e.g QP greater than or equal to a threshold).

In one example, according to the techniques herein, all four boundaries of a block (i.e. left, right, top, bottom) a block boundary may be deblocked when Local Illumination Compensation (LIC) is used for a block and all the transform coefficients for that block is zero and quantization step size is large (e.g QP greater than or equal to a threshold).

In one example, according to the techniques herein, a block boundary may be deblocked when cross component prediction is used for blocks on one (or both) side of a boundary and all the transform coefficients for that block is zero.

In one example, according to the techniques herein, a block boundary may be deblocked when cross component prediction is used for blocks on one (or both) side of a boundary and all the transform coefficients for that block is zero and quantization step size is large (e.g QP greater than or equal to a threshold).

In one example, according to the techniques herein, filter unit 216 may be configured to perform deblocking according to multiple filtering passes. In one example, a filtering pass may correspond to processing/constructing of all/subset of samples to be deblocked. The number of processing/construction(s) for each sample in a given pass may correspond to the pass index/order. The subset of samples to be deblocked may correspond to the pass index/order. In one example, every pass may correspond to processing/constructing of all of samples to be deblocked exactly once. In one example of such a case, deblocked samples from the previous iteration (as well as non-deblocked samples) may be used to construct deblocked samples for current iteration. In one example of such a case, deblocked samples from the previous and current iteration (as well as non-deblocked samples) may be used to construct deblocked samples. In this case, an ordering may be specified for constructing deblocked samples. In one example, the number of iterations may be determined based on one or more of: the slice type; the block size; the skip flags of the current CU and its neighboring CUs; the prediction mode(Intra\inter) of the current CU and its neighboring CUs; the sample position to be de-blocked; whether d<β; and/or the strong or weak filter determination condition provided in JEM described above; distance of sample being deblocked (in number of samples) from boundary; block size(s) on each side of boundary; boundary strength; prediction mode used by blocks on each side of boundary; prediction mode of sample being deblocked; QP of sample being deblocked; block size corresponding to the sample being deblocked; block size corresponding to the samples being used for deblocking; motion vectors for blocks on each side of boundary being deblocked; motion vectors for sample being deblocked; and/or motion vectors for sample being used for deblocking. In one example, the iteration number may determine one or more filter parameters.

In an example, N-pass deblocking with a pre-determined deblocking support may be represented as:

-   -   For iterIdx=0 to (N−1)         -   For pos=posM to posN//samples being deblocked             -   temp[pos]=f_pos(samples values at pass iterIdx in                 deblocking support)         -   For pos=posM to posN             -   Update sampleValue[pos] with temp[pos]     -   Where f_pos( ) is a linear transformation of the form:

${{f\_ pos}\left( {{samples}\mspace{14mu}{values}\mspace{14mu}{at}\mspace{14mu}{pass}\mspace{14mu}{iterIdx}\mspace{14mu}{in}\mspace{14mu}{deblocking}\mspace{14mu}{support}} \right)} = {\sum\limits_{m \in {{deblocking}\mspace{14mu}{support}}}^{\;}{{{coeff\_ pos}\lbrack m\rbrack}{{sampleValue}\left\lbrack {m,{iterIdx}} \right\rbrack}}}$

-   -   with the coeff_pos[ ] being an array of values dependent on         position pos of sample being deblocked. It should be noted, that         each sampleValue[ ] being used may be generated using deblocking         in the previous iteration. Also, the deblocking support does not         change from one iteration to next.     -   Performing an iteration-by-iteration analysis provides:         -   For iterIdx 0, the samples used are the non-deblocked             samples so for each pos:             -   temp [pos]=f_pos(samples values at pass 0 in deblocking                 support).         -   For iterIdx 1,             -   temp[pos]=f_pos(samples values at pass 1 in deblocking                 support).     -   Since f_pos( ) are linear transformations and the deblocking         support does not change, the above can be re-written as:         -   For iterIdx 1,             -   temp[pos]=g_pos(samples values at pass 0 in deblocking                 support).     -   Where g_pos( ) is a linear transformation similar to f_pos( )         that depends on position pos, but with different coefficient         values.     -   This simplification can be performed recursively for each         iteration resulting in a filtering operations that are depends         only on the original sample values at iteration 0 leading to an         equivalent single-pass. Due to finite precision used in some         cases, the final coefficient values may be approximated leading         to an approximate single-pass representation of the multi-pass         filtering operation.

In one example, according to the techniques herein, filter unit 216 may be configured to extend filter lines and the corresponding filter coefficients. In one example, the sample lines to be filtered may be extended to eight at one side. In one example, for line 0 and line 1, the filter coefficients may be {1, 1, 1, 1, 1, 2, 2, 2, 1, 1, 1, 1, 1}/16; for line 2 and line 3, the filter coefficients may be {1, 1, 1, 1, 1, 1, 1, 1}/8; and the filter coefficients for other lines may be {1, 2, 2, 2, 1}/8, where line 0 denotes the nearest sample line to the boundary.

It should be noted that in JEM, the reconstructed samples are always used to filter samples in the deblocking process. In one example, according to the techniques herein, filter unit 216 may be configured to use modified sample values resulting from deblocking to filter other samples values. In one example, modified sample values may be used as inputs when filtering other samples value. In one example, a filtering order may be specified. In one example, a filter order may perform deblocking from the farthest line from boundary to the nearest line.

As described above, deblocked samples are typically clipped to lie within a range of values. The range of values may be based on the original sample value and other parameters received in a bitstream. In an example, the range of values is [original sample value−t_c, original sample value+t_c]. In one example, according to the techniques herein, filter unit 216 may be configured to adjust a clipping function based on one or more of: the sample values in the last one or more rounds in the multiple pass deblocking; a QP value; a slice type; a current prediction mode(Intra/Inter); a current skip flag value; the intra prediction modes of samples to be deblocked; the motion vector of samples to be deblocked; the sample position (e.g., different samples can use different clipping functions); the CU position (e.g., different CU can use different clipping functions); and/or any of the other conditions describe above.

In one example, according to the techniques herein, filter unit 216 may be configured to perform the filtering techniques described herein based on a block size. For example, one or more of the filtering techniques described herein may be applied on a boundary, where the block sizes around the boundary are larger than a threshold. For example, a determination of whether to perform a filtering techniques may be as follows: (1) check each set of 4×4 samples on each side of boundary (i.e., since minimum CU size is 4×4 luma samples); (2) if any one set of 4×4 samples belongs to a CU with size larger than a thresholds (e.g., 64), the filtering technique will be performed on the current boundary. In one example, according to the techniques herein, filter unit 216 may be configured to perform the filtering techniques described herein based on one or more of: slice type; whether a block shape is rectangular; where a block shape is square; the skip flags of the current CU and its neighboring CUs; the prediction mode(Intra\inter) of the current CU and its neighboring CUs; the sample position to be de-blocked.

In one example, according to the techniques herein, filter unit 216 may be configured to perform the wider-stronger luma filtering as follows:

-   -   First, determine whether P-side makes use of large blocks as         follows, as:         bSidePisLargeBlk=((edge type is vertical and p ₀ belongs to         block (e.g. CU) with width>=32)∥(edge type is horizontal and p ₀         belongs to block (e.g. CU) with height>=32))?TRUE:FALSE     -   Next, determine whether Q-side makes use of large blocks as         follows, as:         bSideQisLargeBlk=((edge type is vertical and q ₀ belongs to         block (e.g. CU) with width>=32)∥(edge type is horizontal and q ₀         belongs to block (e.g. CU) with height>=32))?TRUE:FALSE     -   Next, derive the following variables:         d0P=bSidePisLargeBlk?XCalDQpLargeBlock(R[0]):XCalDQp(R[0])         d1P=bSidePisLargeBlk?XCalDQpLargeBlock(R[3]): XCalDQp(R[3])         d0Q=bSideQisLargeBlk?XCalDQqLargeBlock(R[0]):XCalDQq(R[0])         d1Q=bSideQLargeBlk?XCalDQqLargeBlock(R[3]):XCalDQq(R[3])         d0L=d0P+d0Q         d3L=d1P+d1Q         dL=d0L+d3L     -   Next, Condition1 and Condition2 are evaluated as follows:         Condition1=(dL<β)?TRUE:FALSE         Condition2=(xUseStrongFilteringLargeBlock(R[0],d0L,bSidePisLargeBlk,bSideQisLargeBlk)&&xUseStrongFilteringLargeBlock(R[3],d3L,bSidePisLargeBlk,bSideQisLargeBlk))?TRUE:FALSE     -   When Condition1, Condition2 and bSidePisLargeBlk is TRUE then a         wider-stronger filter is applied to the P-side of the boundary         (e.g. WS00P).     -   When Condition1, Condition2 and bSideQisLargeBlk is TRUE then a         wider-stronger filter is applied to the Q-side of the boundary.         (e.g. WS00Q)

In one example, Condition2 may be modified as follows: Condition2=(When block on either side of boundary makes use of Local Illumination Compensation and the CBF of that block is 0)?TRUE: ((xUseStrongFilteringLargeBlock(R[0],d0L,bSidePisLargeBlk,bSideQisLargeBlk)&& xUseStrongFilteringLargeBlock(R[3],d3L,bSidePisLargeBlk,bSideQisLargeBlk))?TRUE:FALSE)

In one example, according to the techniques herein, filter unit 216 may be configured to perform the chroma filtering as follows:

-   -   When, (edge type is vertical and p₀ belongs to CU with         width>=32)∥(edge type is horizontal and p₀ belongs to CU with         height>=32)&&(edge type is vertical and q₀ belongs to CU with         width>=32)∥(edge type is horizontal and q₀ belongs to CU with         height>=32), then a narrow strong filter (e.g NS00P and NS00Q)         may be used,     -   Otherwise, narrow weak filter may be used (e.g. NW00P and         NW00Q).

In one example, according to the techniques herein, filter unit 216 may be configured to perform the chroma filtering as follows:

-   -   When, (p₀ belongs to CU with width>=32 and p₀ belongs to CU with         height>=32)∥(q₀ belongs to CU with width>=32 and q₀ belongs to         CU with height>=32), then a narrow strong filter (e.g NS00P and         NS00Q) may be used, Otherwise, narrow weak filter may be used         (e.g. NW00P and NW00Q).

In one example, according to the techniques herein, filter unit 216 may be configured to perform deblock filtering according to the example flowchart illustrated in FIG. 10 . In one example, filter unit 216 may be configured to perform deblock filtering according to the flowchart illustrated in FIG. 10 for luma samples. FIG. 10 illustrates an example where for a current block (e.g., one of a P block or a Q block) one of the following types of deblocking may be applied: a wide stronger filter, a strong filter, a weak filter, or no filtering. In one example, applying a wide stronger filter may include applying the WS00P and WS00Q filters described above. In one example, applying a strong filter may include applying the HEVC_P and HEVC_Q filters described above. In one example, applying a weak filter may include applying the weak filter in HEVC, described above as Weak Filter. As illustrated in FIG. 10 , a wider stronger filter is applied at 408, no filter is applied at 412, a strong filter is applied 416, and a weak filter is applied at 418 based on whether: a large block condition is true at 402, a large block gradient condition is true at 404, a large block strong filter condition is true at 406, a gradient condition is true at 410, and a strong filter condition is true at 414.

In one example, a large block condition may include whether the following is true: If((EDGE_VER&&(cur_block_width>=32∥adjacent_block_width>=32))∥(EDGE_HOR&&(cur_block_height>=32∥adjacent_block_height>=32)))

-   -   Where     -   EDGE_VER is a vertical boundary type,     -   EDGE_HOR is a horizontal boundary type,     -   cur_block_width is a current block width, e.g., in luma samples,     -   cur_block_height is a current block height, e.g., in luma         samples,     -   adjacent_block_width is an adjacent block width, e.g., in luma         samples, and     -   adjacent_block_height is an adjacent block height, e.g., in luma         samples.

In one example, a large block gradient condition may include whether Condition 1, described above, is true. In one example, a large block strong filter condition may include whether one of the example Condition2, described above, is true.

In one example, a gradient condition may include whether d<β, where d is determined as follows: d0P=XCalDQp(R[0]) d1P=XCalDQp(R[3]) d0Q=XCalDQq(R[0]) d1Q=XCalDQq(R[3]) d0=d0P+d0Q; d3=d1P+d1Q; d=d0+d3;

In one example, a strong filter condition may include whether the following is true: (xUseStrongFilteringLargeBlock(R[0],d0,false,false)&&xUseStrongFilteringLargeBlock(R[3],d3,false,false))?TRUE:FALSE

In one example, according to the techniques herein, filter unit 216 may be configured to perform deblock filtering according to the example flowchart illustrated in FIG. 11 . In one example, filter unit 216 may be configured to perform deblock filtering according to the flowchart illustrated in FIG. 11 for chroma samples. FIG. 11 illustrates an example where for a current block (e.g., P block or a Q block) one of the following types of deblocking may be applied: a wide stronger filter, or a weak filter. In one example, applying a wide stronger filter may include applying the NS00P and NS00Q filters described above. In one example, applying a weak filter may include applying the as NW00P and NW00Q filters described above. As illustrated in FIG. 11 , a wider stronger filter is applied at 504, and a weak filter is applied at 506 based on whether: a large block condition is true at 502.

In one example, a large block condition may include whether the following is true: If((EDGE_VER&&(cur_block_width>=32∥adjacent_block_width>=32))∥(EDGE_HOR&&(cur_block_height>=32∥adjacent_block_height>=32)))

-   -   Where     -   EDGE_VER is a vertical boundary type,     -   EDGE_HOR is a horizontal boundary type,     -   cur_block_width is a current block width, e.g., in chroma         samples,     -   cur_block_height is a current block height, e.g., in chroma         samples,     -   adjacent_block_width is an adjacent block width, e.g., in chroma         samples, and     -   adjacent_block_height is an adjacent block height, e.g., in         chroma samples.

In one example, filter unit 216 may be configured to perform deblock filtering for chroma samples of a P block or a Q block) based on the following condition set: If((EDGE_VER&&(cur_Q_block_width>=TH_w))∥(EDGE_HOR&& (cur_Q_block_height>=TH_h)) is TRUE, apply NS00Q on Q samples. Otherwise, apply a weak filter on Q samples (e.g., NW00Q Q-side filter). If((EDGE_VER&&(cur_P_block_width>=TH_w))∥(EDGE_HOR&&(cur_P_block_height>=TH_h)) is TRUE, apply NS00P on P samples. Otherwise, apply a weak filter on P samples (e.g., NW00P P-side filter).

-   -   Where     -   EDGE_VER is a vertical boundary type,     -   EDGE_HOR is a horizontal boundary type,     -   cur_Q_block_width is a current Q block width, e.g., in chroma         samples,     -   cur_Q_block_height is a current Q block height, e.g., in chroma         samples,     -   cur_P_block_width is a current P block width, e.g., in chroma         samples,     -   cur_P_block_height is a current P block height, e.g., in chroma         samples,     -   TH_w is a width threshold (e.g., 32 samples), and     -   TH_h is a height threshold (e.g., 32 samples).

It should be noted that a threshold value (e.g., TH_w and/or TH_h), in some examples may include a predefined value (e.g., 16 or 32), in some examples may be signaled in a parameter set, in some examples may be signaling in a slice header, and in some examples may be the CTU size in a current portion of video.

Referring to FIG. 11 , in one example, the large block condition may be replaced with a luma filter condition. That is, for example, if a strong filter is applied to a luma block, the wide stronger filter may be applied to the collocated chroma block at 504, otherwise a weak filter may be applied to the collocated chroma block at 506.

In one example, according to the techniques herein, filter unit 216 may be configured to perform deblock filtering according to the example flowchart illustrated in FIG. 12 . In one example, filter unit 216 may be configured to perform deblock filtering according to the flowchart illustrated in FIG. 12 for chroma samples. FIG. 12 illustrates an example where for a current block (e.g., P block or a Q block) one of the following types of deblocking may be applied: a wide stronger filter or a weak filter. In one example, applying a wide stronger filter may include applying the NS00P and NS00Q filters described above. In one example, applying a weak filter may include applying the as NW00P and NW00Q filters described above. As illustrated in FIG. 12 , a wider stronger filter is applied at 608 and a weak filter is applied at 606 based on whether: a large block condition is true at 602 and a large block strong filter condition is true at 604.

In one example, a large block condition may include whether the following is true: If((EDGE_VER&&(cur_block_width>=TH_w&&adjacent_block_width>=TH_w))∥(EDGE_HOR&&(cur_block_height>=TH_h∥adjacent_block_height>=TH_h)))

-   -   Where     -   EDGE_VER is a vertical boundary type,     -   EDGE_HOR is a horizontal boundary type,     -   cur_block_width is a current block width, e.g., in chroma         samples,     -   cur_block_height is a current block height, e.g., in chroma         samples,     -   adjacent_block_width is an adjacent block width, e.g., in chroma         samples, and     -   adjacent_block_height is an adjacent block height, e.g., in         chroma samples     -   TH_w is a width threshold (e.g., 32 samples), and     -   TH_h is a height threshold (e.g., 32 samples).

It should be noted that a threshold value (e.g., TH_w and/or TH_h), in some examples may include a predefined value (e.g., 16 or 32), in some examples may be signaled in a parameter set, in some examples may be signaling in a slice header, and in some examples may be the CTU size in a current portion of video. In one example, a threshold value is larger than 4.

In one example, a wider strong filter condition may include whether both a first condition and a second condition are true. That is, a strong filter condition may be true when both the first condition and the second condition are true. In one example, a first condition may be true when d<β, where d is determined as follows: dp0=xCalcDP(R _(C)[0]); dq0=xCalcDQ(R _(C)[0])); dp1=xCalcDP(R _(C)[1]); dq1=xCalcDQ(R _(C)[1]); d0=dp0+dq0; d1=dp1+dq1; d=d0+d1.

-   -   Where,     -   R_(C)[N] corresponds to chroma lines perpendicular to the edge         being deblocked and at distance N from the top of current chroma         segment being deblocked; and

In one example, a second condition may be true when ((abs(p3−p0)+abs(q3−q0)<(β>3))&&(d<(β>>2))&&(abs(q0−p0)<((tC*5+1)>>1)))

-   -   is true for R_(C)[0] and R_(C)[1].

In one example, a second condition may be true when ((abs(p3−p0)+abs(q3−q0)<(β>3))&&(d<(β>>2))&&(abs(q0−p0)<((tC*5+1)>>1)))

-   -   is true for R_(C)[0].

It should be noted that in one example, an edge is deblocked as segments, where the segment length may be a function of the smallest dimension allowed for a CU/TU/PU/subPU. Further, when 2×N and N×2 CU's are the shortest and thinnest blocks allowed in chroma channel then the chroma segment length may be 2.

It should be noted that according to the chroma filtering above, two lines perpendicular to the edge being deblocked are processed as the basic segment. In one example, four lines may be processed as the basic segment. In one example, when four lines are processed as the basic segment, a first condition may be true when d<β, where d is determined as follows: dp0=xCalcDP(R _(C)[0]); dq0=xCalcDQ(R _(C)[0])); dp3=xCalcDP(R _(C)[3]); dq3=xCalcDQ(R _(C)[3]); d0=dp0+dq0; d3=dp3+dq3; d=d0+d1.

Further, in one example, when four lines are processed as the basic segment, a second condition may be true when ((abs(p3−p0)+abs(q3−q0)<(β>3))&&(d<(β>>2))&&(abs(q0−p0)<((tC*5+1)>>1)))

-   -   is true for R_(C)[0] and R_(C)[3].

As described above, in ITU-T H.265, the deblocking filter may be applied differently to CTU boundaries that coincide with slice and tile boundaries compared with CTU boundaries that do not coincide with slice and tile boundaries. Specifically, in ITU-T H.265, slice_loop_filter_across_slices_enabled_flag enables/disables the deblocking filter across CTU boundaries that coincide with top and left slice boundaries. In one example, according to the techniques herein, when support samples of a deblocking filter exceeds a boundary (e.g., picture/slice/tile) a deblocking filter using the support samples may not be allowed. In one example, according to the techniques herein, when support samples of a deblocking filter exceeds a boundary (e.g., picture/slice/tile) and using sample values across a boundary (e.g., slice) is disabled, a padding operation may be used to generate support sample values. For example, one of: a numeric scalar, circular, replicate, or symmetric padding may be used to generate a support sample, where a numeric scalar padding operation pads according to a constant value, a circular padding operation pads with circular repetition of sample values, a replicate padding operation pads by repeating border sample values, and a symmetric padding operation pads with a mirror reflection of sample values.

As described above, in ITU-T H.265, filtered values are clipped based on a value t_(C). In particular, for the Strong Filter in ITU-T H.265, described above, p_(i)′ values are clipped to (p_(i)−2*t_(C), p_(i)+2*t_(C)) and q_(i)′ values are clipped to (q_(i)−2*t_(C), q_(i)+2*t_(C)). As described above, in ITU-T H.265, the variable t_(C)′ (and thus, the value of t_(C)) is determined based on the index Q which is determined based on qP_(L), which is equal to: (QP_(Q)+QP_(P)+1)/2. In the some cases of video coding, (e.g., proposed techniques for coding high dynamic range (HDR) video), the values of the QP may be changed at CU-level or CTU-level. In these cases, the range of the clipping operation provided in ITU-T H.265 based on index Q may be inadequate. In one example, according to the techniques herein, different values of t_(C)′ may be determined for the P side samples and the Q side samples. That is, a P side t_(C)′ value, t_(CP)′, and a corresponding P side t_(C) value, t_(CP), may be used to clip p_(i)′ values and a Q side t_(C)′ value, t_(CQ)′, and a corresponding Q side t_(C) value, t_(CQ), may be used to clip q_(i)′ values. In one example, respective a P side index Q, Q_(p), and Q side index Q, Q_(q), may be determined by substituting qP_(L) with respective values of QP_(p) and QP_(Q) in the Q index equation above. Thus, according to the techniques herein, p_(i)′ values may be clipped to (p_(i)−2*t_(CP), p_(i)+2*t_(CP)) and q_(i)′ values may be clipped to (q_(i)−2*t_(CQ), q_(i)+2*t_(CQ)). It should be noted that p_(i)′ values and q_(i)′ values may include filtered values generated according to any filter described herein. Thus, the techniques for clipping p_(i)′ values and q_(i)′ values based on respective t_(CP) and t_(CQ) may be applicable to any filter described herein.

It should be noted that in some cases, a video block (e.g., a CU) may include internal TU boundaries and blocking artifacts may appear within the video block. In some cases, when a video block has a dimension larger than 64, deblocking of internal TU boundaries may be disabled. In one example, according to the techniques herein, deblocking may be performed along video block boundaries and also along any internal TU boundaries even in cases where a video block has a dimension larger than 64.

Referring to FIGS. 5A-5B, some cases, a P block or a Q block may include multiple objects. For example, referring to FIG. 5A, in one example, columns p₇ to p₃ may correspond to a first object, columns p₂ to p₀ may correspond to a second object, and columns q₀ to q₇ may correspond to a third object. In such a case, when samples in columns p₂ to p₀ are filtered using samples in one or more column p₃ and q₀ to q₃, as support samples, the resulting filter sample values in columns p₂ to p₀ may appear blurred. Further, in some cases deblocking may lead to smearing of dominant sample value(s) and/or introduce other visual artifacts.

As described above, a corresponding deblocked sample value, y[n] having support samples, may be specified based on the following equation:

${y\lbrack n\rbrack} = {\sum\limits_{m = a}^{b}{{{coeff}\lbrack m\rbrack}{x\left\lbrack {n + m} \right\rbrack}}}$

-   -   Where,     -   A filter length is determined as abs(a−b+1);     -   coeff[m] provides a filter tap value (also referred to as a         filter coefficient);     -   x[n+m] provides input sample values corresponding to support         samples.

In one example, according to the techniques herein, in order to avoid a blurring or an artifact caused by distinct objects being included in filtered samples and support samples, one or more clipping operations may be applied to the term x[n+m]. In one example, the term x[n+m] may be replaced with Clip3(x[n]−2*t_(C), x[n]+2*t_(C), x[n+m]).

-   -   In one example, the term x[n+m] may be modified such that a         support sample x[n+m] is excluded from the summation if         abs(x[n+m]−x[n]) is greater than a threshold. It should be noted         that in the case where coeff[m] corresponds to an average         distribution (i.e., coeff[m]=1/filter length, where filter         length equals (abs(a−b+1))), the coeff[m] is calculated as         1/(filter length−excluded samples). It should be noted that in         the case where coeff[m] corresponds to a Gaussian distribution         (i.e., Σ_(m=a) ^(b) coeff[m]=1, where filter length equals         abs(a−b+1)). In one example, the term x[n+m] may be modified         such that for every support sample x[n+m] where abs(x[n+m]−x[n])         that is greater than a threshold is satisfied, the value of         support sample x[n+m] is substituted with the value of x[n]. It         should be noted that the threshold value may be based on a         combination of one or more of: a predefined value (e.g., 2 or         4), a value signaled in a parameter set, a value signaled in a         slice header, a value based on a QP value (e.g., a QP value of a         current sample and/or a support sample), and/or a value based on         prediction information (e.g., an intra prediction mode and/or         motion information of a current sample and/or a support sample).

In one example, different filters may be applied at different sample positions with respect to a boundary. For example, samples close to the boundary may be filtered using strong filters and samples far from the boundary may be filter using weak filters. For example, samples in column p0 to p1 may be filtered according to a strong filter and samples in columns p2 to p4 may be filtered according to a weak filter. In one example, for chroma deblocking (or luma deblocking), a threshold (e.g., 2, 3, 4) may be used to such that if the positional distance between the current sample and the sample nearest to the boundary is smaller than the threshold, a strong filter will be applied. In one example, the threshold may be based on one or more of: block size on each side of boundary (one or both); boundary strength; prediction mode used by blocks on each side of boundary; prediction mode of sample being deblocked; QP of sample being deblocked; block size corresponding to the sample being deblocked; block size corresponding to the samples being used for deblocking; motion vectors for blocks on each side of boundary being deblocked; motion vectors for sample being deblocked; and/or motion vectors for sample being used for deblocking.

It should be noted that in some cases of video coding, the luminance transform coefficients (e.g., after quantization) corresponding to a CU may be 0, and the CU may be divided into sub-PUs for motion compensation (e.g., ATMVP). In such a case, according to the techniques herein luminance deblocking may be performed along subPU boundaries and further, along the CU boundaries in some examples.

It should be noted that in some cases of video coding, the chrominance transform coefficients (e.g., after quantization) corresponding to a CU may be 0, and the CU may be divided into sub-PUs for motion compensation (e.g., ATMVP). In such a case, according to the techniques herein chrominance deblocking may be performed along sub-PU boundaries and further, along the CU boundaries in some examples.

As described above, in ITU-T H.265, for luma each of Bs, t_(C), β, and d are used to determine which filter type to apply (e.g., Strong Filter or Weak Filter). In particular, if d is less than β, a variable dStrong is determined as follows: d_strong=abs(p ₃ −p ₀)+abs(q ₀ −q ₃)

Whether a Strong Filter or Weak Filter is applied is determined based on the value of d_strong as follows: If ((d_strong<(β>>3))&&(d<(β>>2))&&(abs(p ₀ −q ₀)<than (5*tC+1)>>1),

-   -   The Strong filter is applied;     -   Otherwise,     -   The Weak filter is applied.

In one example, according to the techniques herein dStrong may be determined as follows: d_strong=(bSidePisLarge?max(abs(p ₀ −p ₇),max(abs(p ₃ −p ₀),abs(p ₇ −p ₃))):abs(p ₃ −p ₀))+(bSideQisLarge?Max(abs(q ₀ −q ₇),max(abs(q ₃ −q ₀),abs(q ₇ −q ₃))):abs(q ₃ −q ₀));

With respect to the deblocking filter implementations in JEM, when one of the following conditions is valid, luma deblocking cannot be performed in parallel as indicated below. That is, for example, deblocking may not be performed on both the left and right vertical boundaries of a block or the top and bottom horizontal boundaries of a block in parallel. That is, deblocking cannot be performed on two block boundaries in parallel, as the filtering process for one boundary may involve the samples deblocked by the filtering process for another boundary. Thus, samples at the center of a block may be covered by both of the deblocking filters at each corresponding edge. If (Cur_EDGE_VER&& cur_block_width==4), no parallel deblocking of current block vertical boundaries; If (Cur_EDGE_VER&& adjacent_block_width==4), no parallel deblocking of adjacent block vertical boundaries; If (Cur_EDGE_HOR&& cur_block_height==4), no parallel deblocking of current block horizontal boundaries; If (Cur_EDGE_HOR&& adjacent_block_width==4), no parallel deblocking of adjacent block horizontal boundaries;

-   -   Where,     -   Cur_EDGE_VER is a current vertical boundary,     -   Cur_EDGE_HOR is a current horizontal boundary,     -   cur_block_width is a current block width, e.g., in luma samples,     -   cur_block_height is a current block height, e.g., in luma         samples,     -   adjacent_block_width is an adjacent block width, e.g., in luma         samples, and     -   adjacent_block_height is an adjacent block height, e.g., in luma         samples.

In one example, according to the techniques herein, for each of the conditions above, deblocking may be performed on luma samples at a boundary as follows: If (Cur_EDGE_VER&&cur_block_width==4 && adjacent_block_width>4), for Cur_EDGE_VER only perform deblocking on adjacent block samples; If (Cur_EDGE_VER&&cur_block_width==4&&adjacent_block_width==4), for Cur_EDGE_VER do not perform deblocking; If (Cur_EDGE_VER&&cur_block_width>4 && adjacent_block_width==4), for Cur_EDGE_VER only perform deblocking on current block samples; If (Cur_EDGE_VER&&cur_block_width>4 && adjacent_block_width>4), for Cur_EDGE_VER perform deblocking on current block samples and adjacent block samples; If (Cur_EDGE_HOR&&cur_block_height==4 && adjacent_block_height>4), for Cur_EDGE_HOR only perform deblocking on adjacent block samples; If (Cur_EDGE_HOR&&cur_block_height==4 && adjacent_block_height==4), for Cur_EDGE_HOR do not perform deblocking; If (Cur_EDGE_HOR&&cur_block_height>4 && adjacent_block_height==4), for Cur_EDGE_HOR only perform deblocking on current block samples; If (Cur_EDGE_HOR&&cur_block_height>4 && adjacent_block_height>4), for Cur_EDGE_HOR perform deblocking on current block samples and adjacent block samples.

In a manner similar to that described above, for chroma deblocking, cases where parallel deblocking are limited occur when respective block cur_block_height, adjacent_block_height, cur_block_width, adjacent_block_width are equal to the threshold of 2. Thus, according to the techniques herein, for chroma samples, deblocking may be performed as described above where the threshold value 4 is replaced with the threshold value of 2 in the conditional statements.

In one example, according to the technique herein, instead of not performing deblocking on an edge for a block having dimension less than or equal to a threshold value, a narrower filter may be applied to samples at the edge. For example, in the case where (Cur_EDGE_VER && cur_block_width==4 && adjacent_block_width>4), deblocking may be performed as follows:

-   -   For Cur_EDGE_VER perform deblocking on adjacent block samples         according filter width and perform deblocking on the one         adjacent column of samples at Cur_EDGE_VER for the current         block.

In a similar manner, a narrower filter may be applied to samples at the edge for each of the cases described above. Thus, in general, according to the techniques herein, a video encoder (and/or video decoder) may be configured to determine when parallel deblocking is limited, for example, due to overlapping deblocking filters (e.g., a filter width being greater than half the block's width (or height)), and modify which samples which would otherwise be deblocked. It should be noted that in some cases, parallel deblocking may be limited based on the samples which are used for deblocking support. According to the techniques herein, a video encoder (and/or video decoder) may be configured to determine when parallel deblocking is limited do to samples in a block may being used for deblocking support for multiple deblocking filters.

As described above, for a F4P P-side filter, one of the computations includes: p ₀′=(p ₇ +p ₆ +p ₅ +p ₄ +p ₃ +p ₂ +p ₁+2*p ₀ +q ₀ +q ₁ +q ₂ +q ₃ +q ₄ +q ₅ +q ₆+8)>>4

It should be noted that if a q-side is size 8 and the opposite edge from the current edge makes use of strong HEVC filter then the samples q₅ and q₆ may be modified by the strong HEVC deblocking operation for the opposite side. Parallel processing cannot occur of deblocking edges that are parallel to each other. In one example, to prevent this, the p-side should use long filters (i.e., stronger filters) only if the q-side length (perpendicular to the edge) is greater than or equal to 16. This condition (e.g., LargeBlk condition) be checked in one of the following ways:

-   -   LargeBlk condition: (Both sides of the edge have length         perpendicular to the edge>=16)?TRUE:FALSE;     -   LargeBlk condition: (Both sides of the edge have length         perpendicular to the edge>=32)?TRUE:FALSE;     -   OR     -   LargeBlk condition: (Large block side of the edge has length         perpendicular to the edge>=32 AND other block side of the edge         has length perpendicular to the edge>=16)?TRUE: FALSE. Note,         when both block size length is same then we would require that         both be >=32. Wider-stronger filters are only used for side with         length>=32.

In one example, according to the techniques herein, a set of deblocking filters may make use of a bilinear operation. In one example, block boundary samples p_(i) and q_(i) for i=0 to S−1 are replaced by linear interpolation as follows p _(i)′=(f _(i)*Middle_(s,t)+(64−f _(i))*P _(s)+32)>>6), clipped to p _(i) ±tc q _(i)′=(g _(i)*Middle_(s,t)+(64−g _(i))*Q _(t)+32)>>6), clipped to q _(i) ±tc

In one example, f_(i), Middle_(s,t), P_(s), g_(i), and Q_(t) may be determined as provided in Table 1.

TABLE 1 s, t (p-side, q-side) Filter kernels 7, 7 f_(i) = 59 − i * 9, can also be described as f = {59, 50, 41, 32, 23, 14, 5} g_(i) = 59 − i * 9, can also be described as g = {59, 50, 41, 32, 23, 14, 5} Middle_(7, 7) = (2* (p₀ + q₀) + p₁ + q₁ + p₂ + q₂ + p₃ + q₃ + p₄ + q₄ + p₅ + q₅ + p₆ + q₆ + 8) >> 4 P₇ = (p₆ + p₇ + 1) >> 1, Q₇ = (q₆ + q₇ + 1) >> 1 5, 5 f_(i) = 58 − i * 13, can also be described as f = {58, 45, 32, 19, 6} g_(i) = 58 − i * 13, can also be described as g = {58, 45, 32, 19, 6} Middle_(5, 5) = (2 * (p₀ + q₀ + p₁ + q₁ + p₂ + q₂) + p₃ + q₃ + p₄ + q₄ + 8) >> 4 P₅ = (p₄ + p₅ + 1) >> 1, Q₅ = (q₄ + q₅ + 1) >> 1 3, 3 f_(i) = 53 − i * 21, can also be described as f = {53, 32, 11} g_(i) = 53 − i* 21, can also be described as g = {53, 32, 11} Middle_(3, 3) = (3 * (p₀ + q₀ + p₁ + q₁) + 2 * (p₂ + q₂) + 8) >> 4 P₃ = (p₂ + p₃ + 1) >> 1, Q₃ = (q₂ + q₃ + 1) >> 1 7, 5 f_(i) = 59 − i * 9, can also be described as f = {59, 50, 41, 32, 23, 14, 5} g_(i) = 58 − i * 13, can also be described as g = {58, 45, 32, 19, 6} Middle_(7, 5) = (2 * (p₀ + q₀ + q₁ + q₂) + p₁ + p₂ + p₃ + q₃ + p₄ + q₄ + p₅ + p₆ + 8) >> 4 P₇ = (p₆ + p₇ + 1) >> 1, Q₅ = (q₄ + q₅ + 1) >> 1 7, 3 f_(i) = 59 − i * 9, can also be described as f = {59, 50, 41, 32, 23, 14, 5} g_(i) = 53 − i * 21, can also be described as g = {53, 32, 11} Middle_(7, 3) = (2 * (p₀ + q₀) + q₀ + 2 * (q₁ + q₂) + p₁ + q₁ + p₂ + p₃ + p₄ + p₅ + p₆ + 8) >> 4 P₇ = (p₆ + p₇ + 1) >> 1, Q₃ = (q₂ + q₃ + 1) >> 1 5, 3 f_(i) = 58 − i * 13, can also be described as f = {58, 45, 32, 19, 6} g_(i) = 53 − i * 21, can also be described as g = {53, 32, 11} Middle_(5, 3) = (2 * (p₀ + q₀ + p₁ + q₁ + p₂ + q₂) + q₀ + q₁ + p₃ + p₄ + 8) >> 4 P₅ = (p₄ + p₅ + 1) >> 1, Q₃ = (q₂ + q₃ + 1) >> 1 5, 7 g_(i) = 59 − i * 9, can also be described as g = {59, 50, 41, 32, 23, 14, 5} f_(i) = 58 − i * 13, can also be described as f = {58, 45, 32, 19, 6} Middle_(5, 7) = (2 * (q₀ + p₀ + p₁ + p₂) + q₁ + q₂ + q₃ + p₃ + q₄ + p₄ + q₅ + q₆ + 8) >> 4 Q₇ = (q₆ + q₇ + 1) >> 1, P₅ = (p₄ + p₅ + 1) >> 1 3, 7 g_(i) = 59 − i * 9, can also be described as g = {59, 50, 41, 32, 23, 14, 5} f_(i) = 53 − i * 21, can also be described as f = {53, 32, 11} Middle_(3, 7) = (2 * (q₀ + p₀) + p₀ + 2 * (p₁ + p₂) + q₁ + p₁ + q₂ + q₃ + q₄ + q₅ + q₆ + 8) >> 4 Q₇ = (q₆ + q₇ + 1) >> 1, P₃ = (p₂ + p₃ + 1) >> 1

With respect to Table 1, it should be noted that for 7,5; 7,3; 5,3; 5,7; and 3,7 the weights of p_(i) and q_(i) for Middle are not the same and derived from 7,7 by adding additional terms.

In one example, according to the techniques herein, a set of deblocking filters may make use of a bilinear operation if either side is greater than or equal to 32.

In one example, according to the techniques when either side is greater than or equal to 32 bilinear deblocking may be performed as provided in Table 2.

TABLE 2 P-side Q-side s, t >=32 >=32 7, 7 >=32   <32 7, 3   <32 >=32 3, 7

In one example, according to the techniques when either side is greater than or equal to 32 bilinear deblocking may be performed as provided in Table 3.

TABLE 3 P-side Q-side s, t >=32 >=32 7, 7 >=32   <32 7, 5   <32 >=32 5, 7

In one example, according to the techniques when either side is greater than or equal to 32 bilinear deblocking may be performed as provided in Table 4.

TABLE 4 P-side Q-side s, t >=32 >=32 5, 5 >=32   <32 5, 3   <32 >=32 3, 5

In one example, according to the techniques when either side is greater than or equal to 32 bilinear deblocking may be performed as provided in Table 5.

TABLE 5 P-side Q-side s, t >=32 >=32 7, 7 >=32   <32 7, 3   <32 >=32 3, 7   <32   <32 3, 3

In one example, according to the techniques when either side is greater than or equal to 32 bilinear deblocking may be performed as provided in Table 6.

TABLE 6 P-side Q-side s, t >=32 >=32 7, 7 >=32   <32 7, 5   <32 >=32 5, 7   <32   <32 5, 5

In one example, according to the techniques when either side is greater than or equal to 32 bilinear deblocking may be performed as provided in Table 7.

TABLE 7 P-side Q-side s, t >=32 >=32 5, 5 >=32   <32 5, 3   <32 >=32 3, 5   <32   <32 3, 3

In one example, according to the techniques herein, a set of deblocking filters may make use of a bilinear operation if either side is greater than or equal to 16. In such a case, in Tables 2-7, 32 may be replaced with 16. In one example for Tables 5, 6, and 7, the last column (s,t) of rows with P-side length not equal to Q-side length may make use of (3,3),(5,5),(3,3) respective filtering. In one example, whether a set of deblocking filters makes use of a bilinear operation may be additionally conditioned on whether a strong filter condition is true. For example, any of the strong filter conditions described above. In one example, whether a set of deblocking filters makes use of a bilinear operation may be additionally conditioned as follows:

-   -   The variables dpq0, dpq3, dp, dq, and d are derived as follows:         dp0=abs(p _(2,0)−2*p _(1,0) +p _(0,0))         dp3=abs(p _(2,3)−2*p _(1,3) +p _(0,3))         dq0=abs(q _(2,0)−2*q _(1,0) +q _(0,0))         dq3=abs(q _(2,3)−2*q _(1,3) +q _(0,3))         -   and then,         -   if (p side is greater than or equal to 16)             dp0=(dp0+abs(p _(5,0)−2*p _(4,0) +p _(3,0))+1)>>1             dp3=(dp3+abs(p _(5,3)−2*p _(4,3) +p _(3,3))+1)>>1         -   if (q side is greater than or equal to 16)             dq0=(dq0+Abs(q _(5,0)−2*q _(4,0) +q _(3,0))+1)>>1             dq3=(dq3+Abs(q _(5,3)−2*q _(4,3) +q _(3,3))+1)>>1             dpq0=dp0+dq0             dpq3=dp3+dq3             dp=dp0+dp3             dq=dq0+dq3             d=dpq0+dpq3     -   When d is less than β, the following ordered steps apply:         -   The variable dpq is set equal to 2*dpq0.             sp ₃=abs(p ₃ −p ₀)         -   if (p side is greater than or equal to 16)             sp ₃=(sp ₃+abs(p ₇ −p ₃)+1)>>1             sq ₃=abs(q ₃ −q ₀)             -   if (q side is greater than or equal to 16)                 sq ₃=(sq ₃+abs(q ₇ −q ₃)+1)>>1                 StrongFilterCondition=(dpq is less than (β>>2),sp ₃ +sq                 ₃ is less than (β>>3), and abs(p ₀ −q ₀) is less than                 (5*t _(C)+1)>>1)?TRUE:FALSE

It should be noted that in some examples: control parameter values for luma and chroma (e.g., β, tC, etc.) may not be the same and signaled using different set of syntax elements; control parameter values for chroma may be derived from control parameter values for luma; deblocking may be performed only on subPU edges that align with 8×8 (luma) and 4×4 (chroma) boundary; deblocking of edges of a current block may be based on the usage of linear model (LM) chroma; deblocking of edges of a current block may be based on the usage of separate partitioning trees; deblocking of edges of a current block may be based on the usage of pulse code modulation (PCM); and/or deblocking of edges of a current block may be based on the usage of transform quantization bypass mode. It should be noted that PCM is a lossless coding mode for a block of samples. In an example of PCM coding, samples are directly represented by a predefined number of bits. The bit depth used for PCM may be signaled in parameter set(s).

With respect to deblocking of edges of a current block based on the usage of LM chroma and/or deblocking of edges of a current block may be based on the usage of separate partitioning trees, in one example, deblock may be performed on edges of current block when LM chroma is used for a chroma block and/or separate trees is used for luma and chroma and/or transform coefficients received is zero. With respect to in one example, for separate trees deblocking may be performed only on a chroma edge (e.g. TU edges, PU edges, subPU edges, CU edges) co-incident with a 4×4 chroma grid.

In one example, when the large block condition is not TRUE and the strong filter condition is TRUE then NS00P and NS00Q are used to deblock the edge.

In one example, when the large block condition is not TRUE and the strong filter condition is TRUE then the (s,t)=3,3 filters are used to deblock the edge.

It should be noted that in some cases, a deblocking boundary may include a horizontal CTU boundary. For example, referring to FIG. 5B, in some cases, samples p_(y,x) may be included in the CTU which is above the CTU including samples q_(y,x). For purposes of coding the top line in a current CTU, a typical video coder implementation stores N rows of samples in the bottom lines of the CTU above the current CTU. For example, in the case where the deblocking boundary in FIG. 5B is a CTU boundary, a video coder stores values p_(x,0) for performing intra prediction coding of line q_(x,0). A CTU line buffer refers to the lines of sample values above the current CTU which are stored for coding the current CTU. As the number of lines included in the CTU line buffer increases, memory costs of an video coder implementation increases. It should be noted that in some cases, data corresponding to sample values is also stored (e.g., prediction mode (and associated information e.g., intra prediction mode, bi-pred/uni-pred, motion vectors, reference index, etc.), block size, coefficient coding flags, etc.) Thus, in order to avoid increasing implementation costs, it is desirable to avoid increasing the number of lines included in the CTU line buffer solely for purposes of performing deblocking. For example, if all coding features of a proposed video coding standard require a CTU line buffer to store four lines of sample values, a deblocking filter that requires the CTU line buffer to be increased to store seven lines of sample values would increase implementation costs.

As described above, JEM describes the coding features that are under coordinated test model study by the JVET as potentially enhancing video coding technology beyond the capabilities of ITU-T H.265. Further, in response to a “Joint Call for Proposals on Video Compression with Capabilities beyond HEVC,” jointly issued by VCEG and MPEG, multiple descriptions of video coding were proposed by various groups at the 10th Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, San Diego, CA As a result of the multiple descriptions of video coding, a draft text of a video coding specification is described in “Versatile Video Coding (Draft 1),” 10th Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, San Diego, CA, document JVET-J1001-v2, which is incorporated by reference herein, and referred to as JVET-J1001. “Versatile Video Coding (Draft 2),” 11th Meeting of ISO/IEC JTC1/SC29/WG11 10-18 Jul. 2018, Ljubljana, S I, document JVET-K1001-v4, which is incorporated by reference herein, and referred to as JVET-K1001, is an update to JVET-J1001. Proposed techniques in each of JVET-J1001 and JVET-K1001 are being implemented and evaluated using a Test Model (VTM) and Benchmark Set (BMS). The existing deblocking filter in BMS modifies up to three samples perpendicular to edges.

“CE2-related: Longer Tap Deblocking Filter,” 11th Meeting of ISO/IEC JTC1/SC29/WG11 10-18 Jul. 2018, Ljubljana, S I, document JVET-K0369-r3 which is referred to herein as JVET-K0369, describes a deblocking filter which modifies up to seven samples perpendicular to edges being deblocked. Further, in order to restrict the CTU line buffer size, the filter described in JVET-K0369 restricts the filtering operations for horizontal edges overlapping with CTU boundaries. In particular, JVET-K0369 describes a deblocking filter which modifies sample values according to Table 8A and provides where for the horizontal edges which overlap with the CTU boundaries, the deblocking filter is modified as illustrated in Table 8B.

TABLE 8A Filter coefficients Output {p₇, p₆, p₅, p₄, p₃, p₂, p₁, p₀, Input pixel q₀, q₁, q₂, q₃, q₄, q₅, q₆, q₇} pixels p₆′ {6, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0} p₇ to q₀ p₅′ {5, 1, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0} p₇ to q₁ p₄′ {4, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0} p₇ to q₂ p₃′ {3, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0} p₇ to q₃ p₂′ {2, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0} p₇ to q₄ p₁′ {1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0} p₇ to q₅ p₀′ {1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 0} p₇ to q₆ q₀′ {0, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1} p₆ to q₇ q₁′ {0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1} p₅ to q₇ q₂′ {0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 2} p₄ to q₇ q₃′ {0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 3} p₃ to q₇ q₄′ {0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 4} p₂ to q₇ q₅′ {0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 1, 5} p₁ to q₇ q₆′ {0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 6} p₀ to q₇

TABLE 8B Filter coefficients Output {p₇, p₆, p₅, p₄, p₃, p₂, p₁, p₀, Input pixel q₀, q₁, q₂, q₃, q₄, q₅, q₆, q₇} pixels p₂′ {0, 0, 0, 0, 6, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0} p₃ to q₄ p₁′ {0, 0, 0, 0, 5, 1, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0} p₃ to q₅ p₀′ {0, 0, 0, 0, 5, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 0} p₃ to q₆ q₀′ {0, 0, 0, 0, 4, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1} p₃ to q₇ q₁′ {0, 0, 0, 0, 3, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1} p₃ to q₇ q₂′ {0, 0, 0, 0, 2, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 2} p₃ to q₇ q₃′ {0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 3} p₃ to q₇ q₄′ {0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 4} p₂ to q₇ q₅′ {0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 1, 5} p₁ to q₇ q₆′ {0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 6} p₀ to q₇

It should be noted that modifying the deblocking filter are provided in JVET-K0369 for horizontal edges overlapping with CTU boundaries does not reduce the line buffer requirements for chroma sample values. Further, as illustrated in Table 8B, in addition to “zeroing out” filter coefficients for p₇ to p₄, filter coefficient values are changed for p₃ to q₇. Thus, JVET-K0369 requires storing additional filter sets to be used for filtering CTU boundaries, which requires additional memory for storing the coefficients.

In one example, according to the techniques herein, the usage of a long tap filter, which may include a filter that modifies and/or has a filter support that includes at least three or more lines from p_(x,0) to p_(x,i) may be limited. In one example, for luma and/or chroma deblocking if the following condition is met (EDGE_TYPE is EDGE_HOR && Current Boundary is align with a CTU boundary), a long tap filter is not applied for side P, where EDGE_TYPE is EDGE_HOR indicates the current boundary is a horizontal boundary. In one example, for luma and/or chroma deblocking if the following condition is met (EDGE_TYPE is EDGE_HOR && curPos.y % CTUSize in luma samples==0), a long tap filter is not applied for P, where, curPos.y is the vertical luma position of the current block to be deblocked. In one example, for luma and/or chroma deblocking if the following condition is met (EDGE_TYPE is EDGE_HOR && curPosC.y % CTUSize in chroma samples==0), a long tap filter is not applied for P, where, curPosC.y is the vertical chroma position of the current block to be deblocked. In one example, for luma and/or chroma deblocking if the following condition is met (EDGE_TYPE is EDGE_HOR && Current Boundary is align with a CTU boundary), a long tap filter is not applied for side Q and side P. In one example, for luma and/or chroma deblocking if the following condition is met (EDGE_TYPE is EDGE_HOR && curPos.y % CTUSize in luma samples==0), a long tap filter is not applied for side Q and side P. In one example, for luma and/or chroma deblocking if the following condition is met (EDGE_TYPE is EDGE_HOR && curPosC.y % CTUSize in chroma samples==0), a long tap filter is not applied for side Q and side P. In one example, when a long tap filter is not applied, another filter which modifies fewer samples and/or includes a filter support utilizing fewer lines from p_(x,0) to p_(x,i) (e.g., one, two, or three lines). For example, a weak or strong filters described herein may be applied in cases where a long tap filter is not allowed to be applied. It should be noted that, as provided in ITU-T H.265, the % operand is the modulus operand which provides the remainder of x divided by y.

In one example, when a long tap filter is not applied, sample values beyond a target line buffer threshold (e.g., three or four) may be made not-available and predetermined values may be used for the corresponding sample positions. Table 9 illustrates an example where a long tap filter includes the long tap filter described above with respect to Table 8A and a target line buffer threshold is four. Thus, sample values for p₄ to mare not-available. As illustrated in Table 9, values for p₄ to mare not modified for deblocking. Further, as illustrated in Table 9, p₄ to p₇ the filter coefficients are indicated an NA, which indicates that a sample value for each of p₄ to p₇ is not available in the line buffer. In one example, for each p₄ to p₇, the sample value may be set to the sample value of p₃ and the filter coefficients in Table 8A may be used for deriving modified sample value for p₃′ to q₂′.

TABLE 9 Filter coefficients Output {p₇, p₆, p₅, p₄, p₃, p₂, p₁, p₀, Input pixel q₀, q₁, q₂, q₃, q₄, q₅, q₆, q₇} pixels p₃′ {NA, NA, NA, NA, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0} p₇ to q₃ p₂′ {NA, NA, NA, NA, 1, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0} p₇ to q₄ p₁′ {NA, NA, NA, NA, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 0, 0} p₇ to q₅ p₀′ {NA, NA, NA, NA, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 0} p₇ to q₆ q₀′ {NA, NA, NA, NA, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1} p₆ to q₇ q₁′ {NA, NA, NA, NA, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1} p₅ to q₇ q₂′ {NA, NA, NA, NA, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 2} p₄ to q₇ q₃′ {NA, NA, NA, NA, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 3} p₃ to q₇ q₄′ {NA, NA, NA, NA, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 4} p₂ to q₇ q₅′ {NA, NA, NA, NA, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 1, 5} p₁ to q₇ q₆′ {NA, NA, NA, NA, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 3, 6} p₀ to q₇

Further, in one example, values derived from sample values that are available may be used for the corresponding sample positions. In one example, for each p₄ to p₇, the sample value may be set to the average sample value of p₃ and p₂ and the filter coefficients in Table 8A may be used for deriving modified sample value for p₃′ to q₂′.

In one example, when a long tap filter is not applied, the filtering process may be modified based on the position of a sample being deblocked (e.g., based on whether the sample value is above the CTU horizontal boundary OR within a certain distance of the CTU horizontal boundary) and a corresponding filter which do not access/deblock samples beyond the target line buffer threshold may be selected. For example, with respect to the example illustrated in Table 9, for p₃′ and p₂′ different rules may be applied from deriving sample values for p₄ to p₇.

In one example, when a long tap filter is not applied, the control process may be modified based on the position of a sample being deblocked and a corresponding filter which do not access/deblock samples beyond the target line buffer threshold may be selected. For example, (s=3, t=7) filter of Table 1 for luma, (s=3, t=5) filter of Table 1 for luma, F1P for luma, and/or chroma weak filter for chroma may be selected.

In one example, when a long tap filter is not applied, the deblocking grid may be changed, so that samples beyond the target line buffer threshold are not accessed/deblocked. For example, the deblocking grid may be moved so that the horizontal edge is at a distance of 4 below the horizontal CTU edge.

As described above, in ITU-T H.265, based on the QP values used for coding the CBs including video blocks P and Q (which may be referred to as QP_(P) and QP_(Q)), variables t_(C)′ and β′ are determined. The derivation of the index Q for the luma channel is described above. For the chroma channel, ITU-T H.265, provides if the chroma is equal to 4:2:0, a variable Qp_(C) is determined as specified in the table illustrated in FIG. 13 based on the index qPi as follows: qPi=((Qp _(Q) +Qp _(P)+1)>>1)+cQpPicOffset

-   -   where,         -   cQpPicOffset is a variable specifying the picture-level             chroma quantization parameter offset, and             cQpPicOffset=pps_cb_qp_offset for Cb, and             cQpPicOffset=pps_cr_qp_offset for Cr

It should be noted that in ITU-T H.265, if the chroma format is equal to 4:2:2 or 4:4:4, QpC is set equal to Min(qPi, 51).

For Chroma, t_(c)′ is determined using the table illustrated in FIG. 6A and the index Q which is determined as follows for t_(c)′: Q=Clip3(0,53,Q _(pc)+2*+(slice_tc_offset_div2<<1))

The proposed techniques in each of JVET-J1001 and JVET-K1001 provide where separate partitioning trees may be used for partitioning the luma and chroma channels. In cases where separate partitioning trees are used for partitioning the luma and chroma channels, it may be useful to increase the amount to which a QP value for the chroma channel can be varied with respect to a QP value for the luma channel. That is, for example, respective QP offset values, which may be signaled on a slice level, for the each component of the chroma channel may be increased. It should be noted that ITU-H.265 provides the following chroma channel QP offset syntax elements:

-   -   pps_cb_qp_offset and pps_cr_qp_offset specify the offsets to the         luma quantization parameter Qp′Y used for deriving Qp′Cb and         Qp′Cr, respectively. The values of pps_cb_qp_offset and         pps_cr_qp_offset shall be in the range of −12 to +12, inclusive.         When ChromaArrayType is equal to 0, pps_cb_qp_offset and         pps_cr_qp_offset are not used in the decoding process and         decoders shall ignore their value.     -   slice_cb_qp_offset specifies a difference to be added to the         value of pps_cb_qp_offset when determining the value of the         Qp′Cb quantization parameter. The value of slice_cb_qp_offset         shall be in the range of −12 to +12, inclusive. When         slice_cb_qp_offset is not present, it is inferred to be equal         to 0. The value of pps_cb_qp_offset+slice_cb_qp_offset shall be         in the range of −12 to +12, inclusive.     -   slice_cr_qp_offset specifies a difference to be added to the         value of pps_cr_qp_offset when determining the value of the         Qp′Cr quantization parameter. The value of slice_cb_qp_offset         shall be in the range of −12 to +12, inclusive. When         slice_cr_qp_offset is not present, it is inferred to be equal         to 0. The value of pps_cr_qp_offset+slice_cr_qp_offset shall be         in the range of −12 to +12, inclusive.

Changes to the derivation of chroma QP values may effect chroma channel deblocking in cases where deblocking parameters are based on a QP value. According to the techniques herein the derivation of deblocking parameters based QP value(s) may be modified, e.g., in cases where separate partitioning trees may be used for partitioning the luma and chroma channels.

In one example according to the techniques herein, cQpPicOffset may be derived as follows: cQpPicOffset=pps_cb_qp_offset+slice_cb_qp_offset for Cb, and cQpPicOffset=pps_cr_qp_offset+slice_cr_qp_offset for Cr

In one example, a CU level chroma QP offset value may be signaled (for e.g., during a palette mode coding). The chroma QP derivation used for deblocking may make use of the CU level chroma QP offset. For example, if the variables CuQpOffsetCb and CuQpOffsetCr represent Cb and Cr offset, then the chroma QP offset may be derived as: cQpPicOffset=pps_cb_qp_offset+slice_cb_qp_offset+CuQpOffset_(Cb) for Cb cQpPicOffset=pps_cr_qp_offset+slice_cr_qp_offset+CuQpOffset_(Cr) for Cr

In some cases an additional luma and chroma QP offset value may be used for blocks undergoing a type of processing (e.g., adaptive color transform). These QP offsets may be used for deriving the QP for luma and chroma. As a result, the deblocking processes may depend on the additional luma and chroma QP offsets.

In some examples, when separate partitioning trees are used for partitioning the luma and chroma channels, the chroma QP value may be computed based on partition tree type. For example, in one example, the chroma QP value may be determined as follows: qPi=((Qp _(blk_Q) +QP _(blk_P)+1)>>1)+cQpPicOffset

-   -   where, Qp_(blk_P), Qp_(blk_Q) are luma quantization parameters         corresponding to chroma block on P-side and chroma block on         Q-side respectively.

In one example, Qp_(blk_P) and/or Qp_(blk_Q) may be derived from a combination of one or and/or more of: QP values of multiple corresponding luma blocks; the number of samples of the luma block corresponding to the chroma block; the luma QP value corresponding to a predetermined chroma position. In some examples, Qp_(blk_P) and/or Qp_(blk_Q) may be derived using a function such as, for example, an integer averaging with rounding function, a maximum value function. It should be noted, that it possible to have a partial luma block corresponding to a chroma block. FIGS. 14A-14B illustrate examples of possible luma partitionings corresponding to chroma blocks P and Q, where each of the luma blocks have a QP values QP_X. In the example, illustrated in FIG. 14A the chroma block P is collocated with the luma blocks having QP values QP_1 and QP_3 and the chroma block Q is collocated with the luma blocks having QP values QP_2 and QP_4. In the example, illustrated in FIG. 14B the chroma block P is collocated with the luma blocks having QP values QP_1, QP_3, and QP_5 and the chroma block Q is collocated with the luma blocks having QP values QP_2 and QP_4. In one example, for the example illustrated in FIG. 14A, Qp_(blk_P) and Qp_(blk_Q) may be derived as follows: Qp _(blk_P)=(QP_1+QP_3+1)>>1 Qp _(blk_Q)=(QP_2+QP_4+1)>>1

In one example, for the example illustrated in FIG. 14B, Qp_(blk_P) and Qp_(blk_Q) may be derived as follows: QP _(blk_P)=(QP_1+QP_5+2*QP_3+2)>>1 QP _(blk_Q)=(QP_2+QP_4+1)>>1

In one example, Qp_(blk_P) and/or Qp_(blk_Q) may be derived by identifying a set of chroma positions and for each chroma position identifying a corresponding luma positions. For each, corresponding luma position, a corresponding QP value may be determined. The corresponding QP values may be used to derive Qp_(blk_P) and/or Qp_(blk_Q).

As described above, in one example, a wider strong filter condition may include whether both a first condition and a second condition are true, where a first condition may be true when d<β, where d is determined as follows: dp0=xCalcDP(R _(C)[0]); dq0=xCalcDQ(R _(C)[0])); dp1=xCalcDP(R _(C)[1]); dq1=xCalcDQ(R _(C)[1]); d0=dp0+dq0; d1=dp1+dq1; d=d0+d1.

-   -   Where,     -   R_(C)[N] corresponds to chroma lines perpendicular to the edge         being deblocked and at distance N from the top of current chroma         segment being deblocked; and

In one example, a filter condition may include a condition is that is true when d<β, where d is determined as follows: dp0=xCalcDP(R _(C)[0]); dq0=xCalcDQ(12_(C)[0])); d0=dp0+dq0; d=d0+d1.

In some examples, the condition may be checked for x sample segments of the chroma deblocking boundary (e.g., x=2). This reduces the number of lines which a gradient needs to be computed in the worst-case. It should be noted that in the worst case the first condition would compute gradients (xCalcDQP for every line) whereas the above condition would compute gradients once every 2 lines.

As described above, ITU-T H.265, variables β and t_(C) are used for filtering decisions and clipping operations. For example, β and/or t_(C) are used to determine whether a strong filter is used and/or to clip filtered sample values. It should be noted that in JVET-K1001 the peak signal to noise ratio (PSNR) is higher than a given level of quantization compared to ITU-T H.265. Thus, in some cases, it may be useful to modify β and/or t_(C) in order to modify deblocking strength. That is, if the level of distortion is at a given level of quantization is lower, the amount of perceived blockiness is lower and thus, less deblocking is needed. In one example, β may be modified by as follows: β=β<<n. In one example, β may be modified by as follows: β=β>>n. In one example, t_(C) may be modified by as follows: t_(C)=t_(C)<<n. In one example, t_(C) may be modified by as follows: t_(C)=t_(C)>>n. In one example, n may be determined based on a combination of one or more of: Slice type, QP value, block size, bit depth, intra prediction mode, motion vectors (e.g., magnitude), channel type, and/or component type. For example, in one example, t_(C)=t_(C)>>2 may be used for intra slices and t_(C)=t_(C)>>4 may be used for inter slices. In one example, t_(C)=t_(C)>>2 may be used for the luma component and t_(C)=t_(C)>>4 may be used for chroma components.

“CE2-2.1.1: Long deblocking filters and fixes,” 11th Meeting of ISO/IEC JTC1/SC29/WG11 10-18 Jul. 2018, Ljubljana, S I, document JVET-K0307-v1 which is referred to herein as JVET-K0307, describes longs filters and decisions for the luma component. Based on the filtering techniques described above, the filtering techniques in JVET-K0307 may be modified to enable use of long asymmetric filters. For long asymmetric filters, the number of samples deblocked on the larger block side is greater than that on the smaller block side. The deblocking decision processes to select from this extended filter set are described in detail below. The extended filter set may be used for strong deblocking throughout the deblocking.

In one example, according to the techniques herein, luma stronger filters are used when either side has a large block and a modified strong filter condition is met. In one example, a luma large block corresponds to a width>=32 for a vertical edge, and a height>=32 for a horizontal edge.

In one example, a luma stronger filter may be defined as follows:

-   -   Block boundary samples p_(i) and q_(i) for i=0 to S−1 are then         replaced by linear interpolation as follows:         p _(i)′=(f _(i)*Middle_(s,t)+(64−f _(i))*P _(s)+32)>>6), clipped         to p _(i) ±tc         q _(i)′=(g _(i)*Middle_(s,t)+(64−g _(i))*Q _(t)+32)>>6), clipped         to q _(i) ±tc     -   where f_(i), Middle_(s,t), P_(a) and Q_(s) are given below in         Table 10:

TABLE 10 7, 7 f_(i) = 59 − i * 9, can also be described as f = {59, 50, 41, 32, 23, 14, 5} (p side: 7, g_(i) = 59 − i * 9, can also be described as g = {59, 50, 41, 32, 23, 14, 5} q side: 7) Middle_(7, 7) = (2 * (p₀ + q₀) + p₁ + q₁ + p₂ + q₂ + p₃ + q₃ + p₄ + q₄ + p₅ + q₅ + p₆ + q₆ + 8) >> 4 P₇ = (p₆ + p₇ + 1) >> 1, Q₇ = (q₆ + q₇ + 1) >> 1 7,3 f_(i) = 59 − i * 9, can also be described as f = {59, 50, 41, 32, 23, 14, 5} (p side: 7 g_(i) = 53 − i * 21, can also be described as g = {53, 32, 11} q side: 3) Middle_(7, 3) = (2 * (p₀ + q₀) + q₀ + 2 * (q₁ + q₂) + p₁ + q₁ + p₂ + p₃ + p₄ + p₅ + p₆ + 8) >> 4 P₇ = (p₆ + p₇ + 1) >> 1, Q₃ = (q₂ + q₃ + 1) >> 1 3,7 g_(i) = 59 − i * 9, can also be described as g = {59, 50, 41, 32, 23, 14, 5} (p side: 3 f_(i) = 53 − i * 21, can also be described as f = {53, 32, 11} q side: 7) Middle_(3, 7) = (2 * (q₀ + p₀) + p₀ + 2 * (p₁ + p₂) + q₁ + p₁ + q₂ + q₃ + q₄ + q₅ + q₆ + 8) >> 4 Q₇ = (q₆ + q₇ + 1) >> 1, P₃ = (p₂ + p₃ + 1) >> 1

-   -   It should be noted using 7,7 filters on a step function results         in a nearly uniformly increasing ramp. However, using a 7,3         filter with         Middle_(7,3)=(2*(p₀+q₀)+q₀+2*(q₁+q₂)+p₁+q₁+p₂+p₃+p₄+p₅+p₆+8)>>4         on a step function may not result in a nearly uniformly         increasing ramp. In one example, according to the techniques         herein,         Middle_(7,3)=(2*(p₀+q₀)+2*q₀+3*(q₁+q₂)+p₁+q₁+p₂+p₃+p₄+p_(s)+p₆+8)>>4         and         Middle_(3,7)=(2*(q₀+p₀)+2*p₀+3*(p₁+p₂)+q₁+p₁+q₂+q₃+q₄+q₅+q₆+8)>>4         may be used.

In one example, the control process is further based on gradients computed for two lines of four sample segments; comparison of absolute pixel value difference with tc; and comparison of other absolute pixel value differences with β. More gradients are computed for large block side. The control process may be as follows:

-   -   1. The variables dpq0, dpq3, dp, dq, and d are derived as         follows:         -   dp0, dp3, dq0, dq3 are first derived as in ITU-T H.265         -   dpq0, dpq3, dp, dq, d are then derived as in ITU-T H.265         -   As in ITU-T H.265, When d is less than β, the following             ordered steps apply:             -   a. dpq is derived as in ITU-T H.265.             -   b. sp₃=Abs(p₃−p₀), derived as in ITU-T H.265                 -   if (p side is greater than or equal to 32)                     sp ₃=(sp ₃+Abs(p ₇ −p ₃)+1)>>1             -   c. sq₃=Abs(q₀−q₃), derived as in ITU-T H.265                 -   if (q side is greater than or equal to 32)                     sq ₃=(sq ₃+Abs(q ₇ −q ₃)+1)>>1             -   d. As in ITU-T H.265 derive, StrongFilterCondition=(dpq                 is less than (β>>2), sp₃+sq₃ is less than ((p or q side                 is greater than or equal to 32)?(3*β>>5):(β>>3)), and                 Abs(p₀−q₀) is less than (5*t_(C)+1)>>1)?TRUE:FALSE             -   e. if (p side or q side is greater than or equal to 32)                 Set dSp1,dSp2 to Abs(p ₃ −p ₀)                 Set dSq1,dSq2 to Abs(q ₃ −q ₀)                 -   if (q side is greater than or equal to 32)                     dSq1=abs(q ₄−2*q ₂ +q ₀)                     dSq2=abs(q ₆−2*q ₃ +q ₀)                 -   if (p side is greater than or equal to 32)                     dSp1=abs(p ₄−2*p ₂ +p ₀)                     dSp2=abs(p ₆−2*p ₃ +p ₀)                 -   Compute d_strong1 and d_strong2 as:                     d_strong1=dSp1+dSq1                     d_strong2=dSp2+dSq2                     Compute StrongFilterCondition=(StrongFilterCondition                     &&                     ((d_strong1<((3*beta)>>5))&&(d_strong2<((3*beta)>>5))))?TRUE:FALSE             -   f. When StrongFilterCondition is TRUE, use luma stronger                 filter (may be selected based on block-sizes at edge                 boundary).

In one example, a control process may be as follows:

-   -   The variables dpq0, dpq3, dp, dq, and d are derived as follows:         -   dp0, dp3, dq0, dq3 are first derived as in ITU-T H.265         -   dpq0, dpq3, dp, dq, d are then derived as in ITU-T H.265         -   As in ITU-T H.265, When d is less than (3, the following             ordered steps apply:             -   dpq is derived as in ITU-T H.265.             -   sp₃=Abs(p₃−p₀), derived as in ITU-T H.265                 -   if (p side is greater than or equal to 32 && q side                     is greater than or equal to 16)                     sp ₃=(sp ₃+Abs(p ₇ −p ₃)+1)>>1             -   sq₃=Abs(q₀−q₃), derived as in ITU-T H.265                 -   if (q side is greater than or equal to 32 && p side                     is greater than or equal to 16)                     sq ₃=(sq ₃+Abs(q ₇ −q ₃)+>>1     -   As in ITU-TH.265 derive, StrongFilterCondition=(dpq is less than         (β>>2), sp₃+sq₃ is less than (((p side is greater than or equal         to 32 && q side is greater than or equal to 16)) OR (q side is         greater than or equal to 32 && p side is greater than or equal         to 16))?(3*β>>5):(β>>3)), and Abs(p₀−q₀) is less than         (5*t_(C)+1)>>1)?TRUE:FALSE

It should be noted that with respect to the control processes described herein, in some examples, the term (3*β>>5) may be replaced with the term (2*β>>5).

It should be noted that the conditions (p side is greater than or equal to 32 && q side is greater than or equal to 16) and (q side is greater than or equal to 32 && p side is greater than or equal to 16) determine if a luma stronger filter may be applied. It should be noted that in other examples, additional conditions may be applied (e.g., one or more preceding conditions) may be used to determine if a luma stronger filter may be applied. In one example, additional conditions may be as follows:

-   -   if (p side is greater than or equal to 32 && q side is greater         than or equal to 16)∥(q side is greater than or equal to 32 && p         side is greater than or equal to 16); however for (7,7,7,3,3,7)         the decision process is (p side is greater than or equal to 32∥q         side is greater than or equal to 32). The idea is the lower         threshold selection of 3*β>>5 instead of β>>3 applies for any of         these luma stronger filter preceding decision process.

In one example, according to the techniques describe herein luma may be deblocked according to a 4×4 luma sample grid (or in some examples according to a 8×8 luma sample grid). In this example, luma stronger filters, described above as WS00P P-side filter and WS00Q Q-side filter may be used for large blocks where large block corresponds to width>=32 for a vertical edge, and height>=32 for a horizontal edge and the adjacent block is greater than or equal to 16. The control process may be further based on gradients computed for two lines of 4 sample segments; comparison of absolute pixel value difference with tc; and comparison of other absolute pixel value differences with β, as described in further detail below. Further, when p₀ belongs to CTU above current CTU, the following limited support luma filter provided in Table 8B above may be used.

In some cases, a subset of samples are not accessible. In such cases, a control process using this subset of samples may be affected. This may lead to asymmetry in the computation of a gradient. In some examples, in this cases, another control process may be used.

In one example, the control process may be as follows:

-   -   The variables dpq0, dpq3, dp, dq, and d are derived as follows:         -   dp0, dp3, dq0, dq3 are first derived as in ITU-T H.265             LongTapDeblocking=((p side>=32 && q side>=16)∥(p side>=16 &&             q side>=32)))?TRUE:FALSE             ControlSamplesAccessible=p ₀ belongs to CTU above current             CTU?FALSE:TRUE         -   if (LongTapDeblocking)             -   if (p side is greater than or equal to 32 &&                 ControlSamplesAccessible)                 dp0=(dp0+Abs(p _(5,0)−2*p _(4,0) +p _(3,0))+1)>>1                 dp3=(dp3+Abs(p _(5,3)−2*p _(4,3) +p _(3,3))+1)>>1             -   if (q side is greater than or equal to 32)                 dq0=(dq0+Abs(p _(5,0)−2*q _(4,0) +q _(3,0))+1)>>1                 dq3=(dq3+Abs(p _(5,3)−2*q _(4,3) +p _(3,3))+1)>>1             -   dpq0, dpq3, dp, dq, d are then derived as in ITU-T H.265     -   As in ITU-T H.265, When d is less than 13, the following ordered         steps apply:         -   dpq is derived as in ITU-T H.265.         -   sp₃=Abs(p₃−p₀), derived as in ITU-T H.265             -   if (p side is greater than or equal to 32 &&                 LongTapDeblocking && ControlSamplesAccessible)                 sp ₃=(sp ₃+Abs(p ₇ −p ₃)+1)>>1         -   sq₃=Abs(q₀−q₃), derived as in ITU-T H.265             -   if (q side is greater than or equal to 32 &&                 LongTapDeblocking)                 sq ₃=(sq ₃+Abs(q ₇ −q ₃)+1)>>1         -   As in ITU-T H.265 derive, StrongFilterCondition=(dpq is less             than (β>>2), sp₃+sq₃ is less than             (LongTapDeblocking)?(3*β>>5):(β>>3)), and Abs(p₀−q₀) is less             than (5*t_(C)+1)>>1)?TRUE:FALSE         -   When StrongFilterCondition is TRUE and LongTapDeblocking is             TRUE, use luma stronger filter on the side with length             perpendicular to boundary edge greater than or equal to 32,         -   Otherwise, When StrongFilterCondition is TRUE and             LongTapDeblocking is FALSE, use another strong filter (e.g.             HEVC strong filter HEVC_P, HEVC_Q).

In one example, thresholds used in comparisons may also be based on position. For example, whether the edge being deblocked is aligned with the CTU boundary.

In one example, one of the following may be needed for a 4×4 luma deblocking grid:

-   -   When block width/height is equal to 4 for vertical         edge/horizontal edge respectively and if the HEVC filter on/off         condition (i.e. d<Beta, where d=d₀+d₃ and d₀=d_(p0)+d_(q0) and         d₃=d_(p3)+d_(q3)) is evaluated to true for the respective edge,         then this method would enforce HEVC normal/weak filter with         maximum one sample modification. Therefore the following HEVC         condition is checked|δ|<10(t_(C)) where         δ=(9*(q₀−p₀)−(3*(q₁−p₁)+8>>4, and if the condition is evaluated         to true, then samples p₀ and q₀ are modified, otherwise no         filtering is applied.     -   When block width/height is equal to 4 for vertical         edge/horizontal edge respectively, then a maximum of three         samples are used in filter decision and only one sample is         modified by the filter. i.e. p₂ ^(i) is used to replace p₃ ^(i)         in strong/weak filter condition checks and both strong and weak         filter are only allowed to modify p₀ and q₀

In one example, according to the techniques describe herein chroma may be deblocked according to a 2×2 chroma sample grid (or in some examples according to a 4×4 luma sample grid). In this example, HEVC_P P-side and HEVC_Q Q-side filters described above, may be used. Further, when p₀ belongs to CTU above current CTU, the chroma weak filter described above as NW00P above may be used. In one example, the strong filter may be used when the HEVC luma strong filter condition computed for chroma is TRUE and any of the following conditions is true:

-   -   The edge type is vertical an p₀ belongs to CU with width>=16         (chroma samples) and q₀ belongs to CU with width>=16 (chroma         samples)     -   The edge type is horizontal and p₀ belongs to CU with height>=16         (chroma samples) and q₀ belongs to CU with height>=16 (chroma         samples)

As described above, in ITU-T H.265, a boundary strength (Bs) is determined as one of 0, 1, or 2 for each boundary. As further described above, a draft text of a video coding specification is described in JVET-J1001 and JVET-K1001. “Versatile Video Coding (Draft 3),” 12th Meeting of ISO/IEC JTC1/SC29/WG11 3-12 Oct. 2018, Macao, C N, document JVET-L1001-v1, which is incorporated by reference herein, and referred to as JVET-L1001, is an update to JVET-K1001. JVET-L1001 provides the following with respect to determining a boundary strength value, bS[ ][ ], value:

-   -   The variables xD_(i), yD_(j), xN and yN are derived as follows:         -   If edgeType is equal to EDGE_VER, xD_(i) is set equal to             (i<<3), yD_(j) is set equal to (j<<2), xN is set equal to             Max(0, (nCbW/8)−1) and yN is set equal to (nCbH/4)−1.         -   Otherwise (edgeType is equal to EDGE_HOR), xD_(i) is set             equal to (i<<2), yD_(j) is set equal to (j<<3), xN is set             equal to (nCbW/4)−1 and yN is set equal to Max(0,             (nCbH/8)−1).             -   For xD_(i) with i=0 . . . xN and yD_(j) with j=0 . . .                 yN, the following applies:                 -   If edgeFlags[xD_(i)][yD_(j)] is equal to 0, the                     variable bS[xD_(i)][yD_(j)] is set equal to 0.                 -   Otherwise, the following applies:                 -    The sample values p₀ and q₀ are derived as follows:                 -    If edgeType is equal to EDGE_VER, p₀ is set equal                     to recPicture [xCb+xD_(i)−1][yCb+yD_(j)] and q₀ is                     set equal to recPicture [xCb+xD_(i)][yCb+yD_(j)].                 -    Otherwise (edgeType is equal to EDGE_HOR), p₀ is                     set equal to recPicture [xCb+xD_(i)][yCb+yD_(j)−1]                     and q₀ is set equal to recPicture                     [xCb+xD_(i)][yCb+yD_(j)].                 -    The variable bS[xD_(i)][yD_(j)] is derived as                     follows:                 -    If the sample p₀ or q₀ is in the coding block of a                     coding unit coded with intra prediction mode,                     bS[xD_(i)][yD_(j)] is set equal to 2.                 -    Otherwise, if the block edge is also a transform                     block edge and the sample p₀ or q₀ is in a transform                     block which contains one or more non-zero transform                     coefficient levels, bS[xD_(i)][xD_(j)] is set equal                     to 1.                 -    Otherwise, if one or more of the following                     conditions are true, bS [xD_(i)][yD_(j)] is set                     equal to 1:                 -    For the prediction of the coding subblock                     containing the sample p₀ different reference                     pictures or a different number of motion vectors are                     used than for the prediction of the coding subblock                     containing the sample q₀.                 -    One motion vector is used to predict the coding                     subblock containing the sample p₀ and one motion                     vector is used to predict the coding subblock                     containing the sample q₀, and the absolute                     difference between the horizontal or vertical                     component of the motion vectors used is greater than                     or equal to 4 in units of quarter luma samples.                 -    Two motion vectors and two different reference                     pictures are used to predict the coding subblock                     containing the sample p₀, two motion vectors for the                     same two reference pictures are used to predict the                     coding subblock containing the sample q₀ and the                     absolute difference between the horizontal or                     vertical component of the two motion vectors used in                     the prediction of the two coding subblocks for the                     same reference picture is greater than or equal to 4                     in units of quarter luma samples.                 -    Two motion vectors for the same reference picture                     are used to predict the coding subblock containing                     the sample p₀, two motion vectors for the same                     reference picture are used to predict the coding                     subblock containing the sample q₀ and both of the                     following conditions are true:                 -    The absolute difference between the horizontal or                     vertical component of list 0 motion vectors used in                     the prediction of the two coding subblocks is                     greater than or equal to 4 in quarter luma samples,                     or the absolute difference between the horizontal or                     vertical component of the list 1 motion vectors used                     in the prediction of the two coding subblocks is                     greater than or equal to 4 in units of quarter luma                     samples.                 -    The absolute difference between the horizontal or                     vertical component of list 0 motion vector used in                     the prediction of the coding subblock containing the                     sample p₀ and the list 1 motion vector used in the                     prediction of the coding subblock containing the                     sample q₀ is greater than or equal to 4 in units of                     quarter luma samples, or the absolute difference                     between the horizontal or vertical component of the                     list 1 motion vector used in the prediction of the                     coding subblock containing the sample p₀ and list 0                     motion vector used in the prediction of the coding                     subblock containing the sample q₀ is greater than or                     equal to 4 in units of quarter luma samples.                 -    Otherwise, the variable bS[xD_(i)][yD_(j)] is set                     equal to 0.

With respect to determining boundaries, in one example, a derivation process of a transform block boundary may be as follows:

-   -   Inputs to this process are:         -   a location (xB0, yB0) specifying the top-left sample of the             current block relative to the top-left sample of the current             coding block,         -   a variable nTbW specifying the width of the current block,         -   a variable nTbH specifying the height of the current block,         -   a variable treeType specifying whether a single tree             (SINGLE_TREE) or a dual tree is used to partition the CTUs             and, when a dual tree is used, whether the luma             (DUAL_TREE_LUMA) or chroma components (DUAL_TREE_CHROMA) are             currently processed,         -   a variable filterEdgeFlag,         -   a two-dimensional (nCbW)×(nCbH) array edgeFlags,             maxFilterLengthQ and maxFilterLengthP         -   a variable edgeType specifying whether a vertical (EDGE_VER)             or a horizontal (EDGE_HOR) edge is filtered.     -   Output of this process is the modified two-dimensional         (nCbW)×(nCbH) array edgeFlags, maxLengthQ and maxLengthP.     -   The maximum transform block size maxTbSize is derived as         follows:         maxTbSize=(treeType==DUAL_TREE_CHROMA)?MaxTbSizeY/2:MaxTbSize Y     -   Depending on maxTbSize, the following applies:         -   If nTbW is greater than maxTbSize or nTbH is greater than             maxTbSize, the following ordered steps apply.     -   1. The variables newTbW and newTbH are derived as follows:         newTbW=(nTbW>maxTbSize)?(nTbW/2):nTbW         newTbH=(nTbH>maxTbSize)?(nTbH/2):nTbH     -   2. The derivation process of transform block boundary as         specified in this clause is invoked with the location (xB0,         yB0), the variables nTbW set equal to newTbW and nTbH set equal         to newTbH, the variable filterEdgeFlag, the array edgeFlags,         maxFilterLengthQ, maxFilterLengthP, and the variable edgeType as         inputs, and the output is the modified version of array         edgeFlags, maxFilterLengthQ and maxFilterLengthP.     -   3. If nTbW is greater than maxTbSize, the derivation process of         transform block boundary as specified in this clause is invoked         with the luma location (xTb0, yTb0) set equal to (xTb0+newTbW,         yTb0), the variables nTbW set equal to newTbW and nTbH set equal         to newTbH, the variable filterEdgeFlag, the array edgeFlags,         maxFilterLengthQ, maxFilterLengthP and the variable edgeType as         inputs, and the output is the modified version of array         edgeFlags, maxFilterLengthQ and maxFilterLengthP.     -   4. If nTbH is greater than maxTbSize, the derivation process of         transform block boundary as specified in this clause is invoked         with the luma location (xTb0, yTb0) set equal to (xTb0,         yTb0+newTbH), the variables nTbW set equal to newTbW and nTbH         set equal to newTbH, the variable filterEdgeFlag, the array         edgeFlags, maxFilterLengthQ, maxFilterLengthP and the variable         edgeType as inputs, and the output is the modified version of         array edgeFlags, maxFilterLengthQ and maxFilterLengthP.     -   5. If nTbW is greater than maxTbSize and nTbH is greater than         maxTbSize, the derivation process of transform block boundary as         specified in this clause is invoked with the luma location         (xTb0, yTb0) set equal to (xTb0+newTbW, yTb0+newTbH), the         variables nTbW set equal to newTbW and nTbH set equal to newTbH,         the variable filterEdgeFlag, the array edgeFlags,         maxFilterLengthQ, maxFilterLengthP and the variable edgeType as         inputs, and the output is the modified version of array         edgeFlags, maxFilterLengthQ and maxFilterLengthP.         -   Otherwise, the following applies:         -   If edgeType is equal to EDGE_VER, the value of             edgeFlags[xB0][yB0+k] for k=0 . . . nTbH−1 is derived as             follows:         -   If xB0 is equal to 0, edgeFlags[xB0][yB0+k] is set equal to             filterEdgeFlag.         -   Otherwise, edgeFlags[xB0][yB0+k] is set equal to 1.         -   If edgeFlags[xB0][yB0+k] is equal to 1             -   If nTbW {or “width in luma samples of transform block at                 luma position (xB0, yB0+k)”} is equal to or greater than                 32, maxFilterLengthQ[xB0][yB0+k]=7             -   Otherwise, maxFilterLengthQ[xB0][yB0+k]=3             -   If nTbW [xB0−1][yB0+k] {or “width in luma samples of                 transform block at luma position (xB0−1, yB0+k)”} is                 equal to or greater than 32,                 maxFilterLengthP[xB0][yB0+k]=7             -   Otherwise, maxFilterLengthP[xB0][yB0+k]=3             -   If edgeType is EDGE_HOR and (yB0% CtbSizeY) is equal to                 0, maxFilterLengthCbCr[xB0+k][yB0]=1             -   Otherwise, If width in chroma samples of transform block                 at chroma position (xB0/SubWidthC, yB0/SubHeightC+k) is                 equal to or greater than 8 and width in chroma samples                 of transform block at luma position (xB0−1, yB0+k) is                 equal to or greater than 8,                 maxFilterLengthCbCr[xB0/SubWidthtC][yB0/SubHeightC+k]=3             -   Otherwise, maxFilterLengthCbCr[xB0][yB0+k]=1     -   Otherwise         -   If edgeType is EDGE_HOR and (yB0% CtbSizeY) is equal to 0,             maxFilterLengthCbCr[xB0+k][yB0]=1         -   Otherwise, If width in chroma samples of transform block at             chroma position (xB0, yB0+k) and chroma position (xB0−1,             yB0+k) is equal to or greater than 8,             maxFilterLengthCbCr[xB0][yB0+k]=3         -   Otherwise, maxFilterLengthCbCr[xB0][yB0+k]=1         -   Otherwise (edgeType is equal to EDGE_HOR), the value of             edgeFlags[xB0+k][yB0] for k=0 . . . nTbW−1 is derived as             follows:         -   If yB0 is equal to 0, edgeFlags[xB0+k][yB0] is set equal to             filterEdgeFlag.         -   Otherwise, edgeFlags[xB0+k][yB0] is set equal to 1.         -   If edgeFlags[xB0+k][yB0] is equal to 1, the value of             maxFilterLengthQ[xB0+k][yB0][0], maxFilterLengthP[xB0+k]             [yB0][0] for k=0 . . . nTbW−1 is derived as follows:             -   If nTbH {or “height in luma samples of transform block                 at luma position (xB0, yB0+k)”} is equal to or greater                 than 32, maxFilterLengthQ[xB0+k][yB0]=7             -   Otherwise, maxFilterLengthQ[xB0+k][yB0]=3             -   If nTbH[xB0+k][yB0−1] {or “height in luma samples of                 transform block at luma position (xB0+k, yB0−1)”} is                 equal to or greater than 32,                 maxFilterLengthP[xB0+k][yB0]=7             -   Otherwise, maxFilterLengthP[xB0+k][yB0]=3             -   If edgeType is EDGE_HOR and (yB0% CtbSizeY) is equal to                 0, maxFilterLengthCbCr[xB0+k][yB0]=1             -   Otherwise, If height in chroma samples of transform                 block at luma position (xB0/SubWidthC+k, yB0/SubHeightC)                 is equal to or greater             -   than 8 and height in chroma samples of transform block                 at luma position (xB0/SubWidthtC+k, yB0/SubHeightC—1) is                 equal to or greater than 8,                 maxFilterLengthCbCr[xB0/SubWidthC+k][yB0/SubHeightC]=3             -   Otherwise, maxFilterLengthCbCr[xB0+k][yB0]=1                 -   Otherwise             -   If edgeType is EDGE_HOR and (yB0% CtbSizeY) is equal to                 0, maxFilterLengthCbCr[xB0+k][yB0]=1             -   Otherwise, If height in chroma samples of transform                 block at chroma position (xB0+k, yB0) and at chroma                 position (XB0+k, yB0−1) is equal to or greater than 8,                 maxFilterLengthCbCr[xB0+k][yB0]=3             -   Otherwise, maxFilterLengthCbCr[xB0+k][yB0]=1

With respect to determining boundaries, in one example, a derivation process of a coding subblock boundary may be as follows:

-   -   Inputs to this process are:         -   a location (xCb, yCb) specifying the top-left sample of the             current coding block relative to the top-left sample of the             current picture,         -   a variable nCbW specifying the width of the current coding             block,         -   a variable nCbH specifying the height of the current coding             block,         -   a two-dimensional (nCbW)×(nCbH) array edgeFlags,             maxFilterLengthQ and maxFilterLengthP,         -   a variable edgeType specifying whether a vertical (EDGE_VER)             or a horizontal (EDGE_HOR) edge is filtered.     -   Output of this process is the modified two-dimensional         (nCbW)×(nCbH) array edgeFlags, maxFilterLengthQ and         maxFilterLengthP.     -   The number of coding subblock in horizontal direction numSbX and         in vertical direction numSbY are derived as follows:         -   If CuPredMode[xCb][yCb]==MODE_INTRA, numSbX and numSbY are             both set equal to 1.         -   Otherwise, numSbX and numSbY are set equal to             NumSbX[xCb][yCb] and NumSbY[xCb][yCb], respectively.     -   A variable implicitTU is derived as follows:         -   If nCbW is greater than maxTbSize and nCbH is greater than             maxTbSize and cu_cbf is equal to 1 and maxTbSize is equal to             or larger than 32, implicitTU is set equal to 1 otherwise it             is set equal to 0.     -   When component is luma, depending on the value of edgeType the         following applies:         -   If edgeType is equal to EDGE_VER and numSbX is greater than             1,         -   the following applies for i=1 . . . min((nCbW/8)−1,             numSbX−1), k=0 . . . nCbH−1:             edgeFlags[i*Max(8,nCbW/numSbX)][k]=1(8 861)         -   the following applies for i=0 . . . min((nCbW/8)−1,             numSbX−1), k=0 . . . nCbH−1             If edgeFlags[i*Max(8,nCbW/numSbX)][k] is equal to 1,         -   If i is equal to 0,         -   If nCbW at location (xCb−1,yCb) is greater than or equal to             32,         -   If numSbX at location (xCb−1,yCb) is greater than 1,             maxFilterLengthP[i*Max(8,nCbW/numSbX)][k]=5             Otherwise             maxFilterLengthP[i*Max(8,nCbW/numSbX)][k]=7             Otherwise             maxFilterLengthP[i*Max(8,nCbW/numSbX)][k]=3             maxFilterLengthQ[i*Max(8,nCbW/numSbX)][k]=min(5,maxFilterLengthQ[i*Max(8,nCbW/numSbX)][k])         -   Otherwise if i is equal to maxTbSize/8 and implicitTU is             equal to 1             maxFilterLengthP[i*Max(8,nCbW/numSbX)][k]=5             maxFilterLengthQ[i*Max(8,nCbW/numSbX)][k]=5         -   Otherwise if i is equal to 1 or nCbW/8−1 or (implicitTU is             equal to 1 and (i is equal to (maxTbSize−8)/8 or             (maxTbSize+8)/8))             maxFilterLengthP[i*Max(8,nCbW/numSbX)][k]=2             maxFilterLengthQ[i*Max(8,nCbW/numSbX)][k]=2             Otherwise             maxFilterLengthP[i*Max(8,nCbW/numSbX)][k]             maxFilterLengthQ[i*Max(8,nCbW/numSbX)][k]=3         -   Otherwise if edgeType is equal to EDGE_HOR and numSbY is             greater than 1,         -   The following applies for j=1 . . . min((nCbH/8)−1,             numSbY−1), k=0 . . . nCbW−1:             edgeFlags[k][j*Max(8,nCbH/numSbY)]=1         -   The following applies for j=0 . . . min((nCbH/8)−1,             numSbY−1), k=0 . . . nCbW−1:     -   If edgeFlags[k][j*Max(8, nCbH/numSbY)] is equal to 1         -   If j is equal to 0,         -   If nCbH at location (xCb,yCb−1) is greater than or equal to             32,             -   If numSbY at location (xCb,yCb−1) is greater than 1,                 maxFilterLengthP[k][j*Max(8,nCbH/numSbY)]                 Otherwise                 maxFilterLengthP[k][j*Max(8,nCbH/numSbY)]=7                 Otherwise                 maxFilterLengthP[k][j*Max(8,nCbH/numSbY)]=3                 maxFilterLengthQ[k][j*Max(8,nCbH/numSbY)]=min(5,maxFilterLengthQ[k][j*Max(8,nCbH/numSbY)])             -   Otherwise if j is equal to maxTbSize/8 and implicitTU is                 equal to 1                 maxFilterLengthP[k][j*Max(8,nCbH/numSbY)]=5                 maxFilterLengthQ[k][j*Max(8,nCbH/numSbY)]=5             -   Otherwise if j is equal to 1 or nCbH/8−1 or (implicitTU                 is equal to 1 and ((maxTbSize−8)/8 or (maxTbSize+8)/8))                 maxFilterLengthP[k][j*Max(8,nCbH/numSbY)]=2                 maxFilterLengthQ[k][j*Max(8,nCbH/numSbY)]=2                 Otherwise                 maxFilterLengthP[k][j*Max(8,nCbH/numSbY)]=3                 maxFilterLengthQ[k][j*Max(8,nCbH/numSbY)]=3.

As provided above, transform coefficients in the chroma block are not considered in the derivation of boundary strength in JVET-L1001. Further, in JVET-L1001 chroma deblocking is performed only when the boundary strength is larger than 1 and in ITU-T H.265 chroma deblocking is performed only when the boundary strength is equal to 2 which means chroma deblocking is only performed when a P-side or Q-side block is an intra block. “CE11: Long-tap deblocking filter for luma and chroma (CE11.1.6),” 12th Meeting of ISO/IEC JTC1/SC29/WG11 3-12 Oct. 2018, Macao, C N, document JVET-L0327-v1, which is referred to herein as JVET-L0327, describes where chroma deblocking is performed when the boundary strength is 2, or when the boundary strength is 1 for a large block boundary, where a large block boundary occurs when the block size at both the P-side and Q-side are larger than a threshold. It should be noted that in JVET-L0327 the derivation of boundary strength as provided in ITU-T H.265 is used with an additional condition that when the current block has non-zero coefficients on the current component, the boundary strength for that block when deblocking the current component will be larger than 0. “CE11: Long deblocking filters for luma (CE11.1.1) and for both luma and chroma (CE11.1.9),” 12th Meeting of ISO/IEC JTC1/SC29/WG11 3-12 Oct. 2018, Macao, C N, document JVET-L0072, which is referred to herein as JVET-L0072, describes where chroma deblocking is performed when the boundary strength is 2, or when the boundary strength is 1 for an inter block. It should be noted that in JVET-L0072 the derivation of boundary strength as provided in ITU-T H.265 is used with an additional condition that when the current block has non-zero coefficients on the current component, the boundary strength for that block when deblocking the current component will be 1.

According to the techniques herein, in one example, the chroma deblocking may only be performed when the boundary strength is 2 or the boundary is strength is 1 and the chroma block at P-side or Q-side has non-zero coefficients. The derivation of boundary strength may be as provided in ITU-T H.265 with zero or more additional conditions or as provided in JVET-L1001. In particular, deblocking on a Cb (or Cr) block can be performed only when the boundary strength is larger than 1 or the cbf flag of that Cb (or Cr) block is non-zero or the cbf flag of the neighboring block at P-side of that Cb (or Cr) block is non-zero (i.e., the block has at least one non-zero coefficient).

In one example, according to the techniques herein, boundary strength for chroma, ucBs may be derived as follows:

-   -   ucBS=0;     -   cbf=0;         if         (TU::getCbf(tuQ,COMPONENT_Y)∥TU::getCbf(tuP,COMPONENT_Y))cbf|=(1<<0);         if         (TU::getCbf(tuQ,COMPONENT_Cb)∥TU::getCbf(tuP,COMPONENT_Cb))cbf|=(1<<1);         if         (TU::getCbf(tuQ,COMPONENT_Cr)∥TU::getCbf(tuP,COMPONENT_Cr))cbf|=(1<<2);     -   if (cbf)         ucBs=cbf+3;//distinguish with the case ucBS=2     -   where,     -   getCbf gets the cbf flag of a component (specified by the second         input parameter) in a TU (corresponding to first parameter). The         cbf flag equal to 0 means there is no non-zero coefficients in         the TU for the component;     -   A|=B represents A=A|B, where = is an assign operation and | is a         bitwise OR operation; tuP and tuQ represent the TU for P and Q         side respectively for the segment of samples under         consideration;     -   COMPONENT_Y, COMPONENT_Cb, COMPONENT_Cr represent identifiers         for Y, Cb and Cr component respectively.

Further, in this case, chroma deblocking may be performed as follows: If (ucBs==2∥(ucBs>2&&(((ucBs−3)>>(chromaIdx+1))&0x1))//chromaIdx=0

-   -   when component is Cb and chromaIdx=1 when component is Cr,         -   Deblocking can be performed         -   Otherwise,         -   Deblocking cannot be performed         -   Where,         -   0x1 is hexadecimal one and & is a bitwise and operation.

Further, in one example, chroma deblocking for a single tree vertical edge may be performed as follows:

-   -   1. The variable xN is set equal to Max(0, (nCbW/8)−1) and yN is         set equal to Max(0, (nCbH/8)−1).     -   2. The variable edgeSpacing is set equal to 8/SubWidthC.     -   3. The variable edgeSections is set equal to yN*(2/SubHeightC).     -   4. For xD_(k) equal to k*edgeSpacing with k=0 . . . xN and         yD_(m) equal to m<<2 with m=0 . . . edgeSections, the following         applies:         -   When (bS[xD_(k)*SubWidthC][yD_(m)*SubHeightC] is equal to 2             or (bS[xD_(k)*SubWidthC][yD_(m)*SubHeightC] is equal to 1             and nCbW (e.g. width in chroma samples) for coding block at             both location (xCb/SubWidthC, yCb/SubHeightC) and             (xCb/SubWidthC−1, yCb/SubHeightC) is greater than or equal             to 8)) and (((xCb/SubWidthC+xD_(k))>>3)<<3) is equal to             xCb/SubWidthC+xD_(k), the following ordered steps apply:             -   a. The decision process for chroma block edges as                 specified below is invoked with treeType, the picture                 sample array recPicture set equal to the chroma picture                 sample array recPicture_(Cb), the location of the chroma                 coding block (xCb/SubWidthC, yCb/SubHeightC), the chroma                 location of the block (xD_(k), yD_(m)), a variable                 edgeType set equal to EDGE_VER, the boundary filtering                 strength bS[xD_(k)][yD_(m)], and the bit depth bD set                 equal to BitDepth_(Cb) as inputs, and the decisions dE,                 dEp and dEq, and the variable t_(C) as outputs.             -   b. The filtering process for chroma block edges as                 specified below is invoked with the chroma picture                 sample array recPicture_(Cb), the location of the chroma                 coding block (xCb/SubWidthC, yCb/SubHeightC), the chroma                 location of the block (xD_(k), yD_(m)), a variable                 edgeType set equal to EDGE_VER and a variable                 cQpPicOffset set equal to pps_cb_qp_offset as inputs,                 and the modified chroma picture sample array                 recPicture_(Cb) as output.             -   c. The decision process for chroma block edges as                 specified below is invoked with treeType, the picture                 sample array recPicture set equal to the chroma picture                 sample array recPicture_(Cr), the location of the chroma                 coding block (xCb/SubWidthC, yCb/SubHeightC), the chroma                 location of the block (xD_(k), yD_(m)), a variable                 edgeType set equal to EDGE_VER, the boundary             -   filtering strength bS[xD_(k)][yD_(m)], and the bit depth                 bD set equal to BitDepth_(Cr) as inputs, and the                 decisions dE, dEp and dEq, and the variable t_(C) as                 outputs.             -   d. The filtering process for chroma block edges as                 specified below is invoked with the chroma picture                 sample array recPicture_(Cr), the location of the chroma                 coding block (xCb/SubWidthC, yCb/SubHeightC), the chroma                 location of the block (xD_(k), yD_(m)), a variable                 edgeType set equal to EDGE_VER and a variable                 cQpPicOffset set equal to pps_cb_qp_offset as inputs,                 and the modified chroma picture sample array                 recPicture_(Cr) as output.

Further, in one example, chroma deblocking for a single tree horizontal edge may be performed as follows:

-   -   1. The variable xN is set equal to Max(0, (nCbW/8)−1) and yN is         set equal to Max(0, (nCbH/8)−1).     -   2. The variable edgeSpacing is set equal to 8/SubHeightC.     -   3. The variable edgeSections is set equal to xN*(2/SubWidthC).     -   4. For yD_(m) equal to m*edgeSpacing with m=0 . . . yN and         xD_(k) equal to k<<2 with k=0 . . . edgeSections, the following         applies:         -   When (bS[xD_(k)*SubWidthC][yD_(m)*SubHeightC] is equal to 2,             or (bS[xD_(k)*SubWidthC yD_(m)*SubHeightC] is equal to 1 and             nCbH (e.g. height in chroma samples) for coding block at             both location (xCb/SubWidthC, yCb/SubHeightC)_(an)d             (xCb/SubWidthC, yCb/SubHeightC−1) is greater than or equal             to 8)) and (((yCb/SubHeightC+yD_(m))>>3)<<3) is equal to             yCb/SubHeightC+yD_(m), the following ordered steps apply:             -   a. The decision process for chroma block edges as                 specified below is invoked with treeType, the picture                 sample array recPicture set equal to the chroma picture                 sample array recPicture_(Cb), the location of the chroma                 coding block (xCb/SubWidthC, yCb/SubHeightC), the chroma                 location of the block (xD_(k), yD_(m)), a variable                 edgeType set equal to EDGE_HOR, the boundary filtering                 strength bS[xD_(k)][yD_(m)], and the bit depth bD set                 equal to BitDepth_(Cb) as inputs, and the decisions dE,                 dEp and dEq, and the variable t_(C) as outputs.             -   b. The filtering process for chroma block edges as                 specified below is invoked with the chroma picture                 sample array recPicture_(Cb), the location of the chroma                 coding block (xCb/SubWidthC, yCb/SubHeightC), the chroma                 location of the block (xD_(k), yD_(m)), a variable                 edgeType set equal to EDGE_HOR and a variable                 cQpPicOffset set equal to pps_cb_qp_offset as inputs,                 and the modified chroma picture sample array                 recPicture_(Cb) as output.             -   c. The decision process for chroma block edges as                 specified below is invoked with treeType, the picture                 sample array recPicture set equal to the chroma picture                 sample array recPicture_(Cr), the location of the chroma                 coding block (xCb/SubWidthC, yCb/SubHeightC), the chroma                 location of the block (xD_(k), yD_(m)), a variable                 edgeType set equal to EDGE_HOR, the boundary filtering                 strength bS[xD_(k)][yD_(m)], and the bit depth bD set                 equal to BitDepth_(Cr) as inputs, and the decisions dE,                 dEp and dEq, and the variable t_(C) as outputs.             -   d. The filtering process for chroma block edges as                 specified below is invoked with the chroma picture                 sample array recPicture_(Cr), the location of the chroma                 coding block (xCb/SubWidthC, yCb/SubHeightC), the chroma                 location of the block (xD_(k), yD_(m)), a variable                 edgeType set equal to EDGE_HOR and a variable                 cQpPicOffset set equal to pps_cr_qp_offset as inputs,                 and the modified chroma picture sample array                 recPicture_(Cr) as output.

In one example, the decision process for chroma block edges may be as follows:

-   -   This process is only invoked when ChromaArrayType is not equal         to 0.     -   Inputs to this process are:         -   a chroma picture sample array s′,         -   a chroma location (xCb, yCb) specifying the top-left sample             of the current chroma coding block relative to the top-left             chroma sample of the current picture,         -   a chroma location (xB1, yB1) specifying the top-left sample             of the current chroma block relative to the top-left sample             of the current chroma coding block,         -   a variable edgeType specifying whether a vertical (EDGE_VER)             or a horizontal (EDGE_HOR) edge is filtered,         -   a variable cQpPicOffset specifying the picture-level chroma             quantization parameter offset.     -   Outputs of this process are         -   the variables dE, dEp and dEq containing decisions,         -   the variable tC.     -   If edgeType is equal to EDGE_VER, the values p_(i) and q_(i)         with i=0 . . . 1 and k=0 . . . 3 are derived as follows:         q _(i,k) =s′[xCb+xB1+i][yCb+yB1+k]         p _(i,k) =s′[xCb+xB1−i−1][yCb+yB1+k]     -   Otherwise (edgeType is equal to EDGE_HOR), the sample values         p_(i) and q_(i) with i=0 . . . 1 and k=0 . . . 3 are derived as         follows:         q _(i,k) =s′[xCb+xB1+k][yCb+yB1+i]         p _(i,k) =s′[xCb+xB1+k][yCb+yB1−i−1]     -   The variables Qp_(Q) and Qp_(P) are set equal to the Qp_(Y)         values of the coding units which include the coding blocks         containing the sample q_(0,0) and p_(0,0), respectively.     -   If ChromaArrayType is equal to 1, the variable Qp_(C) is         determined as specified in the Table illustrate in FIG. 6B based         on the index qPi derived as follows:         qPi=((Qp _(Q) +Qp _(P)+1)>>1)+cQpPicOffset     -   Otherwise (ChromaArrayType is greater than 1), the variable         Qp_(C) is set equal to Min(qPi, 63).     -   The value of the variable t_(C)′ is determined as specified in         the Table illustrate in FIG. 6B based on the chroma quantization         parameter Q derived as follows:         Q=Clip3(0,65,QP _(C)+2+(slice_tc_offset_div2<<1))     -   where slice_tc_offset_div2 is the value of the syntax element         slice_tc_offset_div2 for the slice that contains sample q_(0,0).     -   The variable t_(C) is derived as follows:         t _(C) =t _(C)′*(1<<(BitDepth_(C)−8))     -   Depending on the value of edgeType, the following applies:         -   If edgeType is equal to EDGE_VER, the following ordered             steps apply:             -   1. The variables dpq0, dpq1, dp, dq and d are derived as                 follows:                 dp0=Abs(p _(2,0)−2*p _(1,0) +p _(0,0))                 dp1=Abs(p _(2,1)−2*p _(1,1) +p _(0,1))                 dq0=Abs(q _(2,0)−2*q _(1,0) +q _(0,0))                 dq1=Abs(q _(2,1)−2*q _(1,1) +q _(0,1))                 dpq0=dp0+dq0                 dpq1=dp1+dq1                 dp=dp0+dp1                 dq=dq0+dq1                 d=dpq0+dpq1             -   2. The variables dE, dEp and dEq are set equal to 0.             -   3. When d is less than β, the following ordered steps                 apply:                 -   a. The variable dpq is set equal to 2*dpq0.                 -   b. For the sample location (xCb+xB1, yCb+yB1), the                     decision process for a chroma sample as specified                     below is invoked with sample values p_(0,0),                     p_(3,0), q_(0,0), and q_(3,0), the variables dpq, β                     and t_(C) as inputs, and the output is assigned to                     the decision dSam0.                 -   c. The variable dpq is set equal to 2*dpq1.                 -   d. For the sample location (xCb+xB1, yCb+yB1+3), the                     decision process for a chroma sample as specified                     below is invoked with sample values p_(0,1),                     p_(3,1), q_(0,1), and q_(3,1), the variables dpq, β                     and t_(C) as inputs, and the output is assigned to                     the decision dSam1.                 -   e. The variable dE is set equal to 1.                 -   f. When dSam0 is equal to 1 and dSam1 is equal to 1,                     the variable dE is set equal to 2.                 -   g. When dp is less than (β+(β>>1))>>3, the variable                     dEp is set equal to 1.                 -   h. When dq is less than (β+(β>>1))>>3, the variable                     dEq is set equal to 1.         -   Otherwise (edgeType is equal to EDGE_HOR), the following             ordered steps apply:             -   1. The variables dpq0, dpq3, dp, dq and d are derived as                 follows:                 dp0=Abs(p _(2,0)−2*p _(1,0) +p _(0,0))                 dp1=Abs(p _(2,1)−2*p _(1,1) +p _(0,1))                 dq0=Abs(q _(2,0)−2*q _(1,3) +q _(0,0))                 dq3=Abs(q _(2,1)−2*q _(1,1) +q _(0,1))                 dpq0=dp0+dq0                 dpq1=dp1+dq1                 dp=dp0+dp1                 dq=dq0+dq1                 d=dpq0+dpq1             -   2. The variables dE, dEp and dEq are set equal to 0.             -   3. When d is less than 13, the following ordered steps                 apply:                 -   a. The variable dpq is set equal to 2*dpq0.                 -   b. For the sample location (xCb+xB1, yCb+yB1), the                     decision process for a chroma sample as specified                     below is invoked with sample values p_(0,0),                     p_(1,0), q_(0,0) and q_(1,3), the variables dpq, β                     and t_(C) as inputs, and the output is assigned to                     the decision dSam0.                 -   c. The variable dpq is set equal to 2*dpq1.                 -   d. For the sample location (xCb+xB1+3, yCb+yB1), the                     decision process for a chroma sample as specified                     below is invoked with sample values p_(0,1),                     p_(3,1), q_(0,1) and q_(3,1), the variables dpq, β                     and t_(C) as inputs, and the output is assigned to                     the decision dSam1.                 -   e. The variable dE is set equal to 1.                 -   f. When dSam0 is equal to 1 and dSam1 is equal to 1,                     the variable dE is set equal to 2.                 -   g. When dp is less than (β+(β>>1))>>3, the variable                     dEp is set equal to 1.     -   When dq is less than (+(β>>1))>>3, the variable dEq is set equal         to 1.

In one example, the decision process for a chroma sample may be as follows:

-   -   Inputs to this process are:         -   the sample values p₀, p₃, q₀ and q₃,         -   the variables dpq, β and t_(C).     -   Output of this process is the variable dSam containing a         decision.         -   The variable dSam is specified as follows:         -   If dpq is less than (β>>2), Abs(p₃−p₀)+Abs(q₀−q₃) is less             than (β>>3) and Abs(p₀−q₀) is less than (5*t_(C)+1)>>1, dSam             is set equal to 1.             -   Otherwise, dSam is set equal to 0.

In one example, the filtering process for chroma block edges may be as follows:

-   -   This process is only invoked when ChromaArrayType is not equal         to 0.     -   Inputs to this process are:         -   a chroma picture sample array s′,         -   a chroma location (xCb, yCb) specifying the top-left sample             of the current chroma coding block relative to the top-left             chroma sample of the current picture,         -   a chroma location (xB1, yB1) specifying the top-left sample             of the current chroma block relative to the top-left sample             of the current chroma coding block,         -   a variable edgeType specifying whether a vertical (EDGE_VER)             or a horizontal (EDGE_HOR) edge is filtered,         -   a variable cQpPicOffset specifying the picture-level chroma             quantization parameter offset.     -   Output of this process is the modified chroma picture sample         array s′.     -   Depending on the value of edgeType, the following applies:         -   If edgeType is equal to EDGE_VER, for each sample location             (xCb+xB1, yCb+yB1+k), k=0 . . . 3, the following ordered             steps apply:         -   1. The filtering process for a chroma sample as specified             below is invoked with the sample values p_(i,k), q_(i,k),             with i=0 . . . 1, the locations (xCb+xB1−1, yCb+yB1+k) and             (xCb+xB1, yCb+yB1+k) and the variable t_(C) as inputs, and             the filtered sample values p₀′ and q₀′ as outputs.         -   2. The filtered sample values p₀′ and q₀′ replace the             corresponding samples inside the sample array s′ as follows:             s′[xCb+xB1][yCb+yB1+k]=q ₀′             s′[xCb+xB1−1][yCb+yB1+k]=p ₀′         -   Otherwise (edgeType is equal to EDGE_HOR), for each sample             location (xCb+xB1+k, yCb+yB1), k=0 . . . 3, the following             ordered steps apply:             -   1. The filtering process for a chroma sample as                 specified below is invoked with the sample values                 p_(i,k), q_(i,k), with i=0 . . . 1, the locations                 (xCb+xB1+k, yCb+yB1−1) and (xCb+xB1+k, yCb+yB1), and the                 variable t_(C) as inputs, and the filtered sample values                 p₀′ and q₀′ as outputs.             -   2. The filtered sample values p₀′ and q₀′ replace the                 corresponding samples inside the sample array s′ as                 follows:                 s′[xCb+xB1+k][yCb+yB1]=q ₀′                 s′[xCb+xB1+k][yCb+yB1−1]=p ₀′

In one example, the filtering process for a chroma sample may be as follows:

-   -   This process is only invoked when ChromaArrayType is not equal         to 0.     -   Inputs to this process are:         -   the chroma sample values p_(i) and q_(i) with i=0 . . . 3,         -   the chroma locations of p_(i) and q_(i), (xP_(i), yP_(i))             and (xQ_(i), yQ_(i)),         -   a variable t_(C).     -   Outputs of this process are:         -   the number of filtered samples nDp and nDq,         -   the filtered sample values p: and with i=0 . . . nDp−1, j=0             . . . nDq−1.     -   Depending on the value of dE, the following applies:         -   If the variable dE is equal to 2, nDp and nDq are both set             equal to 3 and the following strong filtering applies:             p ₀′=Clip3(p ₀ −t _(C) ,p ₀ +t _(C),(p ₃ +p ₂ +p ₁+2*p ₀ +q             ₀ +q ₁ +q ₂+4)>>3)             p ₁′=Clip3(p ₁ −t _(C),(2*p ₃ +p ₂₊₂ *p ₁ +p ₀ +q ₀ +q             ₁+4)>>3)             p ₂′=Clip3(p ₂ −t _(C) ,p ₂ +t _(C),(3*p ₃+2*p ₂ +p ₁ +p ₀             +q ₀+4)>>3)             q ₀′=Clip3(q ₀ −t _(C) ,q ₀ +t _(C),(p ₂ +p ₁ +p ₀+2*q ₀ +q             ₁ +q ₂ +q ₃+4)>>3)             q ₁′=Clip3(q ₁ −t _(C) ,q ₁ +t _(C),(p ₁ +p ₀ +q ₀+2*q ₁ +q             ₂+2*q ₃+4)>>3)             q ₂′=Clip3(q ₂ −t _(C) ,q ₂ +t _(C),(p ₀ +q ₀ +q ₁+2*q ₂+3*q             ₃+4)>>3)             -   Otherwise, nDp and nDq are set both equal to 0 and the                 following weak filtering applies: Δ=Clip3(−t_(C), t_(C),                 ((((q₀−p₀)<<2)+p₁−q₁+4)>>3))                 p ₀′=Clip1_(C)(p ₀+Δ)                 q ₀′=Clip1_(C)(q ₀−Δ)

Further, in one example, luma deblocking for vertical edge may be performed as follows:

-   -   When treeType is equal to SINGLE_TREE or DUAL_TREE_LUMA, the         filtering process for edges in the luma coding block of the         current coding unit consists of the following ordered steps:         -   1. The variable xN is set equal to Max(0, (nCbW/8)−1) and yN             is set equal to (nCbH/4)−1.         -   2. For xD_(k) equal to k<<3 with k=0 . . . nN and yD_(m)             equal to m<<2 with m=0 . . . yN, the following applies:             -   When bS[xD_(k)][yD_(m)] is greater than 0, the following                 ordered steps apply:                 -   a. The decision process for block edges as specified                     in clause below is invoked with treeType, the                     picture sample array recPicture set equal to the                     luma picture sample array recPicture_(L), the                     location of the luma coding block (xCb, yCb), the                     luma location of the block (xD_(k), yD_(m)), a                     variable edgeType set equal to EDGE_VER, the                     boundary filtering strength bS[xD_(k)][yD_(m)], the                     max filter lengths maxFilterLengthP[xD_(k)][yD_(m)]                     and maxFilterLengthQ[xD_(k)][yD_(m)] and the bit                     depth bD set equal to BitDepth_(Y) as inputs, and                     the decisions dE, dEp and dEq, the max filter                     lengths maxFilterLengthP and maxFilterLengthQ, and                     the variable t_(C) as outputs.                 -   b. The filtering process for block edges as                     specified in clause below is invoked with the                     picture sample array recPicture set equal to the                     luma picture sample array recPicture_(L), the                     location of the luma coding block (xCb, yCb), the                     luma location of the block (xD_(k), yD_(m)), a                     variable edgeType set equal to EDGE_VER, the                     decisions dE, dEp and dEq, the max filter lengths                     maxFilterLengthP and maxFilterLengthQ and the                     variable t_(C) as inputs, and the modified luma                     picture sample array recPicture_(L) as output.

Further, in one example, luma deblocking for horizontal edge may be performed as follows:

-   -   When treeType is equal to SINGLE_TREE or DUAL_TREE_LUMA, the         filtering process for edges in the luma coding block of the         current coding unit consists of the following ordered steps:         -   1. The variable yN is set equal to Max(0, (nCbH/8)−1) and xN             is set equal to (nCbW/4)−1.         -   2. For yD_(m) equal to m<<3 with m=0 . . . yN and xD_(k)             equal to k<<2 with k=0 . . . xN, the following applies:             -   When bS[xD_(k)][yD_(m)] is greater than 0, the following                 ordered steps apply:                 -   a. The decision process for block edges as specified                     below is invoked with treeType, the picture sample                     array recPicture set equal to the luma picture                     sample array recPicture_(L), the location of the                     luma coding block (xCb, yCb), the luma location of                     the block (xD_(k), yD_(m)), a variable edgeType set                     equal to EDGE_HOR, the boundary filtering strength                     bS[xD_(k)] [yD_(m)], the max filter lengths                     maxFilterLengthP[xD_(k)][yD_(m)] and                     maxFilterLengthQ[xD_(k)][yD_(m)], and the bit depth                     bD set equal to BitDepth_(y) as inputs, and the                     decisions dE, dEp and dEq, the max filter lengths                     maxFilterLengthP and maxFilterLengthQ, and the                     variable t_(C) as outputs.                 -   b. The filtering process for block edges as                     specified below is invoked with the picture sample                     array recPicture set equal to the luma picture                     sample array recPicture_(L), the location of the                     luma coding block (xCb, yCb), the luma location of                     the block (xD_(k), yD_(m)), a variable edgeType set                     equal to EDGE_HOR, the decisions dEp, dEp and dEq,                     the max filter lengths maxFilterLengthP and                     maxFilterLengthQ, and the variable t_(C) as inputs,                     and the modified luma picture sample array                     recPicture_(L) as output.

In one example, the decision process for luma block edges may be as follows:

-   -   Inputs to this process are:         -   a variable treeType specifying whether a single tree             (SINGLE_TREE) or a dual tree is used to partition the CTUs             and, when a dual tree is used, whether the luma             (DUAL_TREE_LUMA) or chroma components (DUAL_TREE_CHROMA) are             currently processed,         -   a picture sample array recPicture,         -   a location (xCb, yCb) specifying the top-left sample of the             current coding block relative to the top-left sample of the             current picture,         -   a location (xB1, yB1) specifying the top-left sample of the             current block relative to the top-left sample of the current             coding block,         -   a variable edgeType specifying whether a vertical (EDGE_VER)             or a horizontal (EDGE_HOR) edge is filtered,         -   a variable bS specifying the boundary filtering strength,         -   a variable maxFilterLengthP specifying the max filter length             on P side         -   a variable maxFilterLengthQ specifying the max filter length             on Q side         -   a variable bD specifying the bit depth of the current             component.     -   Outputs of this process are:         -   the variables dE, dEp and dEq containing decisions,         -   the variables maxFilterLengthP and maxFilterLengthQ with             modified filter lengths for P and Q side respectively         -   the variable t_(C).     -   If edgeType is equal to EDGE_VER, the sample values p_(i,k) and         q_(j,k) with i=0 . . . maxFilterLengthP and j=0 . . .         maxFilterLengthQ and k=0 and 3 are derived as follows:         q _(i,k)=recPicture_(L) [xCb+xB1+i][yCb+yB1+k]         p _(i,k)=recPicture_(L) [xCb+xB1−i−1][yCb+yB1+k]     -   Otherwise (edgeType is equal to EDGE_HOR), the sample values         p_(i,k) and q_(j,k) with i=0 . . . maxFilterLengthP and j=0 . .         . maxFilterLengthQ and k=0 and 3 are derived as follows:         q _(i,k)=recPicture[xCb+xB1+k][yCb+yB1+i]         p _(i,k)=recPicture[xCb+xB1+k][yCb+yB1−i−1]         -   The variable qpOffset is derived as follows:         -   If sps_ladf_enabled_flag is equal to 1 and treeType is equal             to SINGLE_TREE or DUAL_TREE_LUMA, the following applies:         -   The variable lumaLevel of the reconstructed luma level is             derived as follow:             lumaLevel=((p0,0+p0,3+q0,0+q0,3)>>2),         -   The variable gpOffset is set equal to             sps_ladf_lowest_interval_qp_offset and modified as follows:

for( i = 0; i < sps_num_ladf_intervals_minus2 + 1; i++ ) { if( lumaLevel > SpsLadfIntervalLowerBound[ i + 1 ]) qpOffset = sps_ladf_qp_offset[ i ] else break }

-   -   -   Otherwise (treeType is equal to DUAL_TREE_CHROMA), qpOffset             is set equal to 0.

    -   The variables Qp_(Q) and Qp_(P) are derived as follows:         -   If treeType is equal to SINGLE_TREE or DUAL_TREE_LUMA,             Qp_(Q) and Qp_(P) are set equal to the Qp_(Y) values of the             coding units which include the coding blocks containing the             sample q_(0,0) and p_(0,0), respectively.         -   Otherwise (treeType is equal to DUAL_TREE_CHROMA), Qp_(Q)             and Qp_(P) are set equal to the Qp_(C) values of the coding             units which include the coding blocks containing the sample             q_(0,0) and p_(0,0), respectively.

    -   The variable qP is derived as follows:         qP=((Qp _(Q) +Qp _(P)+1)>>1)+qpOffset

    -   The value of the variable 13′ is determined as specified in         Table 8-18 based on the quantization parameter Q derived as         follows:         Q=Clip3(0,63,qP+(slice_beta_offset_div2<<1))

    -   where slice_beta_offset_div2 is the value of the syntax element         slice_beta_offset_div2 for the slice that contains sample         q_(0,0).

    -   The variable β is derived as follows:         β=β′*(1<<(bD−8))

    -   The value of the variable t_(C)′ is determined as specified in         the Table illustrated in FIG. 6B based on the quantization         parameter Q derived as follows:         Q=Clip3(0,65,qP+2*(bS−1)+(slice_tc_offset_div2<<1))

    -   where slice_tc_offset_div2 is the value of the syntax element         slice_tc_offset_div2 for the slice that contains sample q_(0,0).

    -   The variable t_(C) is derived as follows:         t _(C) =t _(C)′*(1<<(bD−8))

    -   Depending on the value of edgeType, the following applies:         -   If edgeType is equal to EDGE_VER, the following ordered             steps apply:             -   1. The variables dp0, dp3, dq0 and dq3 are derived as                 follows.                 dp0=Abs(p _(2,0)−2*p _(1,0) +p _(0,0))                 dp3=Abs(p _(2,3)−2*p _(1,3) +p _(0,3))                 dq0=Abs(q _(2,0)−2*q _(1,0) +q _(0,0))                 dq3=Abs(q _(2,3)−2*q _(1,3) +q _(0,3))             -   2. The variables bSidePisLargeBlk and bSideQisLargeBlk                 are derived as follows:                 -   If p_(0,0) belongs to coding block with width in                     luma samples greater than or equal to 32,                     bSidePisLargeBlk is set equal to 1 otherwise                     bSidePisLargeBlk is set equal to 0.                 -   If q_(0,0) belongs to coding block with width in                     luma samples greater than or equal to 32,                     bSideQisLargeBlk is set equal to 1 otherwise                     bSideQisLargeBlk is set equal to 0.             -   3. If both bSidePisLargeBlk and bSideQisLargeBlk is                 equal to 0 go to step 6.             -   4. The variables dpq0L, dpq3L and dL are derived as                 follows:                 -   If bSidePisLargeBlk is equal to 1                     dp0L=(dp0+Abs(p _(5,0)−2*p _(4,0) +p _(3,0))+1)>>1                     dp3L=(dp3+Abs(p _(5,3)−2*p _(4,3) +p _(3,3))+1)>>1                     Otherwise                     dp0L=dp0                     dp3L=dp3                 -   If bSideQisLargeBlk is equal to 1                     dq0L=(dq0+Abs(q _(5,0)−2*q _(4,0) +q _(3,0))+1)>>1                     dq3L=(dq3+Abs(q _(5,3)−2*q _(4,3) +q _(3,3))+1)>>1                     Otherwise                     dq0L=dq0                     dq3L=dq3                     dpq0L=dp0L+dq0L                     dpq3L=dp3L+dq3L                     dL=dpq0L+dpq3L             -   5. If dL is less than β, the following ordered steps                 apply otherwise go to step 6:                 -   a. The variable dpq is set equal to 2*dpq0L.                 -   b. The variables sp0, sq0 and spq0 are derived as                     follows:                     sp0=Abs(p _(3,0) −p _(0,0))                     sq0=Abs(q _(0,0) −q _(3,0))                     spq0=Abs(p _(0,0) −q _(0,0))                 -   c. The variable sp is set equal to sp0, the variable                     sq is set equal to sq0 and the variable spq is set                     equal to spq0.                 -   d. When bSidePisLargeBlk is equal to 1 or                     bSidePisLargeBlk is equal to 1, the sample values p₀                     p₃ q₀ and q₃ are derived as follows                 -    If bSidePisLargeBlk                     p ₃ =p _(0,3)                     p ₀ =p _(0,maxFilterLengthP)                 -    If bSideQisLargeBlk                     q ₃ =q _(0,3)                     q ₀ =q _(0,maxFilterLengthQ)                 -    Otherwise, set p₀ p₃ q₀ and q₃ to 0                 -   e. For the sample location (xCb+xB1, yCb+yB1), the                     decision process for a sample as specified below                     invoked with sample values p₀, p₁, q₀, and q₃, dpq,                     sp, sq, spq, bSidePisLargeBlk, bSideQisLargeBlk, β                     and t_(C) as inputs, and the output is assigned to                     the decision dSam0.                 -   f. The variable dpq is set equal to 2*dpq3L.                 -   g. The variables sp3, sq3 and spq3 are derived as                     follows:                     sp3=Abs(p _(3,3) −p _(0,3))                     sq3=Abs(q _(0,3) −q _(3,3))                     spq3=Abs(p _(0,3) −q _(0,3))                 -   h. The variable sp is set equal to sp3, the variable                     sq is set equal to sq3 and the variable spq is set                     equal to spq3.                 -   i. When bSidePisLargeBlk is equal to 1 or                     bSidePisLargeBlk is equal to 1, the sample values p₀                     p₃ q₀ and q₃ are derived as follows                 -    If bSidePisLargeBlk                     p ₃ =p _(3,3)                     p ₀ =p _(3,maxFilterLengthP)                 -    If bSideQisLargeBlk                     q ₃ =q _(3,3)                     q ₀ =q _(3,maxFilterLengthQ)                 -    Otherwise, set p₀ p₃ q₀ and q₃ to 0                 -   j. For the sample location (xCb+xB1, yCb+yB1+3), the                     decision process for a sample as specified below is                     invoked with sample values p_(a), p₃, q₀ and q₃, the                     variables dpq, sp, sq, spq, bSidePisLargeBlk,                     bSideQisLargeBlk, β and t_(C) as inputs, and the                     output is assigned to the decision dSam3.                 -   k. When dSam0 is equal to 1 and dSam3 is equal to 1,                     the variable dE is set equal to 3 and omit steps 6                     to 8.             -   6. The variables maxFilterLengthP, maxFilterLengthQ,                 dpq0, dpq3, dp, dq and d are derived as follows:                 dpq0=dp0+dq0                 dpq3=dp3+dq3                 dp=dp0+dp3                 dq=dq0+dq3                 d=dpq0+dpq3                 maxFilterLengthP=3                 maxFilterLengthQ=3             -   7. The variables dE, dEp and dEq are set equal to 0.             -   8. When d is less than β, the following ordered steps                 apply:                 -   a. The variable dpq is set equal to 2*dpq0.                 -   b. For the sample location (xCb+xB1, yCb+yB1), the                     decision process for a sample as specified below is                     invoked with sample values 0, 0, 0, and 0, the                     variables dpq, sp, sq, spq, bSidePisLargeBlk,                     bSideQisLargeBlk, β and t_(C) as inputs, and the                     output is assigned to the decision dSam0.                 -   c. The variable dpq is set equal to 2*dpq3.                 -   d. For the sample location (xCb+xB1, yCb+yB1+3), the                     decision process for a sample as specified below is                     invoked with sample values 0, 0, 0, and 0, the                     variables dpq, sp, sq, spq, bSidePisLargeBlk,                     bSideQisLargeBlk, β and t_(C) as inputs, and the                     output is assigned to the decision dSam3.                 -   e. The variable dE is set equal to 1.                 -   f. When dSam0 is equal to 1 and dSam3 is equal to 1,                     the variable dE is set equal to 2.                 -   g. When dp is less than (β+(β>>1))>>3, the variable                     dEp is set equal to 1.                 -   h. When dq is less than (β+(β>>1))>>3, the variable                     dEq is set equal to 1.         -   Otherwise (edgeType is equal to EDGE_HOR), the following             ordered steps apply:             -   1. The variables dp0, dp3, dq0 and dq3 are derived as                 follows                 dp0=Abs(p _(2,0)−2*p _(1,0) +p _(0,0))                 dp3=Abs(p _(2,3)−2*p _(1,3) +p _(0,3))                 dq0=Abs(q _(2,0)−2*q _(1,0) +q _(0,0))                 dq3=Abs(q _(2,3)−2*q _(1,3) +q _(0,3))             -   2. The variables bSidePisLargeBlk and bSideQisLargeBlk                 are derived as follows:                 -   If edgeType is EDGE_HOR, and y position of luma                     position of sample p0,0 modulo                 -   CtbSizeY is 0, set bSidePisLargeBlk is set to 0                 -   Otherwise, If p_(0,0) belongs to coding block with                     height greater than or equal to 32,                 -   bSidePisLargeBlk is set equal to 1 otherwise                     bSidePisLargeBlk is set equal to 0.                 -    If q_(0,0) belongs to coding block with height                     greater than or equal to 32,                 -   bSideQisLargeBlk is set equal to 1 otherwise                     bSideQisLargeBlk is set equal to 0.             -   3. If both bSidePisLargeBlk and bSideQisLargeBlk is                 equal to 0 go to step 6.             -   4. The variables dpq0L, dpq3L and dL are derived as                 follows:                 -   If bSidePisLargeBlk is equal to 1                     dp0L=(dp0+Abs(p _(5,0)−2*p _(4,0) +p _(3,0))+1)>>1                     dp3L=(dp3+Abs(p _(5,3)−2*p _(4,3) +p _(3,3))+1)>>1                     Otherwise                     dp0L=dp0                     dp3L=dp3                 -    If bSideQisLargeBlk is equal to 1                     dq0L=(dq0+Abs(q _(5,0)−2*q _(4,0) +q _(3,0))+1)>>1                     dq3L=(dq3+Abs(q _(5,3)−2*q _(4,3) +q _(3,3))+1)>>1                     Otherwise                     dq0L=dq0                     dq3L=dq3                     dpq0L=dp0L+dq0L                     dpq3L=dp3L+dq3L                     dL=dpq0L+dpq3L             -   5. When dL is less than β, the following ordered steps                 apply otherwise go to step 6:                 -   a. The variable dpq is set equal to 2*dpq0L.                 -   b. The variables sp0, sq0 and spq0 are derived as                     follows:                     sp0=Abs(p _(3,0) −p _(0,0))                     sq0=Abs(q _(0,0) −q _(3,0))                     spq0=Abs(p _(0,0) −q _(0,0))                 -   c. The variable sp is set equal to sp0, the variable                     sq is set equal to sq0 and the variable spq is set                     equal to spq0.                 -   d. When bSidePisLargeBlk is equal to 1 or                     bSidePisLargeBlk is equal to 1, the variable p₀ p₃                     q₀ and q₃ are derived as follows                 -    If bSidePisLargeBlk                     p ₃ =p _(0,3)                     p ₀ =p _(0,maxFilterLength) P                 -    If bSideQisLargeBlk                     q ₃ =q _(0,3)                     q ₀ =q _(0,maxFilterLength) Q                 -    Otherwise, set p₀ p₃ q₀ and q₃ to 0                 -   e. For the sample location (xCb+xB1, yCb+yB1), the                     decision process for a sample as specified in clause                     below is invoked with sample values p₀, p₃, q₀ and                     q₃, the variables dpq, sp, sq, spq,                     bSidePisLargeBlk, bSideQisLargeBlk, β and t_(C) as                     inputs, and the output is assigned to the decision                     dSam0.                 -   f. The variable dpq is set equal to 2*dpq3L.                 -   g. The variables sp3, sq3 and spq3 are derived as                     follows:                     sp3=Abs(p _(3,3) −p _(0,3))                     sq3=Abs(q _(0,3) −q _(3,3))                     spq3=Abs(p _(0,3) −q _(0,3))                 -   h. The variable sp is set equal to sp3, the variable                     sq is set equal to sq3 and the variable spq is set                     equal to spq3.                 -   i. When bSidePisLargeBlk is equal to 1 or                     bSidePisLargeBlk is equal to 1, the variable p₀, p₃,                     q₀ and q₃ are derived as follows                 -    If bSidePisLargeBlk                     p ₃ =p _(3,3)                     p ₀ =p _(3,maxFilterLength) P                 -    If bSideQisLargeBlk                     q ₃ =q _(3,3)                     q ₀ =q _(3,maxFilterLength) Q                 -    Otherwise, set to p₀, p₃, q₀ and q₃ to 0                 -   j. For the sample location (xCb+xB1+3, yCb+yB1), the                     decision process for a sample as specified in clause                     below is invoked with sample values p₀, p₃, q₀ and                     q₃, the variables dpq, sp, sq, spq,                     bSidePisLargeBlk, bSideQisLargeBlk, β and t_(C) as                     inputs, and the output is assigned to the decision                     dSam3.                 -   k. When dSam0 is equal to 1 and dSam3 is equal to 1,                     the variable dE is set equal to 3 and omit steps 6                     to 8.             -   6. The variables maxLengthP, maxLengthQ, dpq0, dpq3, dp,                 dq and d are derived as follows:                 dpq0=dp0+dq0                 dpq3=dp3+dq3                 dp=dp0+dp3                 dq=dq0+dq3                 d=dpq0+dpq3                 maxLengthP=3                 maxLengthQ=3             -   7. The variables dE, dEp and dEq are set equal to 0.             -   8. When d is less than β, the following ordered steps                 apply:                 -   a. The variable dpq is set equal to 2*dpq0.                 -   b. For the sample location (xCb+xB1, yCb+yB1), the                     decision process for a sample as specified in clause                     below is invoked with sample values 0, 0, 0 and 0,                     the variables dpq, sp, sq, spq, bSidePisLargeBlk,                     bSideQisLargeBlk, β and t_(C) as inputs, and the                     output is assigned to the decision dSam0.                 -   c. The variable dpq is set equal to 2*dpq3.                 -   d. For the sample location (xCb+xB1+3, yCb+yB1), the                     decision process for a sample as specified in clause                     below is invoked with sample values 0, 0, 0 and 0,                     the variables dpq, sp, sq, spq, bSidePisLargeBlk,                     bSideQisLargeBlk, β and t_(C) as inputs, and the                     output is assigned to the decision dSam3.                 -   e. The variable dE is set equal to 1.                 -   f. When dSam0 is equal to 1 and dSam3 is equal to 1,                     the variable dE is set equal to 2.                 -   g. When dp is less than (β+(β>>1))>>3, the variable                     dEp is set equal to 1.                 -   h. When dq is less than (β+(β>>1))>>3, the variable                     dEq is set equal to 1.

It should be noted that variable CtbSizeY may be defined as follows: The array size for each luma CTB in both width and height is CtbSizeY in units of samples. The width and height of the array for each chroma CTB are CtbWidthC and CtbHeightC, respectively, in units of samples.

In one example, the decision process for a luma sample may be as follows:

-   -   Inputs to this process are:         -   the sample values p₀, p₃, q₀ and q₃,         -   the variables sp, sq, dpq, β and t_(C), bSidePisLargeBlk and             bSideQisLargeBlk.     -   Output of this process is the variable dSam containing a         decision.     -   The variables sp and sq are modified as follows:     -   If bSidePisLargeBlk         sp=(sp+Abs(p ₃ −p ₀)+1)>>1     -   If bSideQisLargeBlk         sq=(sq+Abs(q ₃ −q ₀)+1)>>1     -   The variable sthr is derived as follows:     -   If bSidePisLargeBlk or bSidePisLargeBlk         sthr=3*β>>5         Otherwise         sthr=β>>3     -   The variable dSam is specified as follows:         -   If dpq is less than (β>>2), sp+sq is less than sthr and spq             is less than (5*t_(C)+1)>>1, dSam is set equal to 1.         -   Otherwise, dSam is set equal to 0.

In one example, the filtering process for luma block edges may be as follows:

-   -   Inputs to this process are:         -   a picture sample array recPicture,         -   a location (xCb, yCb) specifying the top-left sample of the             current coding block relative to the top-left sample of the             current picture,         -   a location (xB1, yB1) specifying the top-left sample of the             current block relative to the top-left sample of the current             coding block,         -   a variable edgeType specifying whether a vertical (EDGE_VER)             or a horizontal (EDGE_HOR) edge is filtered,         -   the variables dE, dEp and dEq containing decisions,         -   the variables maxLengthP and maxLengthQ containing filter             lengths,         -   the variable t_(C).     -   Output of this process is the modified picture sample array         recPicture.     -   Depending on the value of edgeType, the following applies:         -   If edgeType is equal to EDGE_VER, the following ordered             steps apply:             -   1. The sample values p_(i,k) and q_(j,k) with i=0 . . .                 maxLengthP, j=0 . . . maxLengthQ and k=0 . . . 3 are                 derived as follows:                 Q _(j,k)=recPicture_(L) [xCb+xB1+j][yCb+yB1+k]                 p _(i,k)=recPicture_(L) [xCb+xB1−i−1][yCb+yB1+k]             -   2. When dE is not equal to 0 and dE is not equal to 3,                 for each sample location (xCb+xB1, yCb+yB1+k), k=0 . . .                 3, the following ordered steps apply:                 -   a. The filtering process for a luma sample as                     specified below is invoked with the sample values                     p_(i,k), q_(i,k) with i=0 . . . 3, the locations                     (xP_(i), yP_(i)) set equal to (xCb+xB1−i−1,                     yCb+yB1+k) and (xQ_(i), yQ_(i)) set equal to                     (xCb+xB1+i, yCb+yB1+k) with i=0 . . . 2, the                     decision dE, the variables dEp and dEq and the                     variable t_(C) as inputs, and the number of filtered                     samples nDp and nDq from each side of the block                     boundary and the filtered sample values p_(i)′ and                     q_(j)′ as outputs.                 -   b. When nDp is greater than 0, the filtered sample                     values p_(i)′ with i=0 . . . nDp−1 replace the                     corresponding samples inside the sample array                     recPicture as follows:                     recPicture[xCb+xB1−i−1][yCb+yB1+k]=p _(i)′                 -   c. When nDq is greater than 0, the filtered sample                     values q_(j)′ with j=0 . . . nDq−1 replace the                     corresponding samples inside the sample array                     recPicture as follows:                     recPicture[xCb+xB1+j][yCb+yB1+k]=q _(j′)             -   3. When dE is equal to 3, for each sample location                 (xCb+xB1, yCb+yB1+k), k=0 . . . 3, the following ordered                 steps apply:                 -   a. The filtering process for a luma sample using                     long filters below is invoked with the sample values                     p_(i,k), q_(j,k) with i=0 . . . maxFilterLengthP and                     j=0 . . . maxFilterLengthQ, the locations (xP_(i),                     yP_(i)) set equal to (xCb+xB1−i−1, yCb+yB1+k) and                     (xQ_(j), yQ_(j)) set equal to (xCb+xB1+j, yCb+yB1+k)                     with i=0 . . . maxFilterLengthP−1 and j=0 . . .                     maxFilterLengthQ−1, the variables maxFilterLengthP,                     maxFilterLengthQ and t_(C) as inputs and the                     filtered samples values p_(i)′ and q_(j)′ as                     outputs.                 -   b. With the filtered sample values n′ with i=0 . . .                     maxFilterLengthP−1 replace the corresponding samples                     inside the sample array recPicture as follows:                     recPicture[xCb+xB1−i−1][yCb+yB1+k]=p _(i)′                 -   c. With the filtered sample values q: with j=0 . . .                     maxFilterLengthQ−1 replace the corresponding samples                     inside the sample array recPicture as follows:                     recPicture[xCb+xB1+j][yCb+yB1+k]=q _(j)′         -   Otherwise (edgeType is equal to EDGE_HOR), the following             ordered steps apply:             -   1. The sample values p_(i,k) and q_(j,k) with i=0 . . .                 maxLengthP, j=0 . . . maxLengthQ and k=0 . . . 3 are                 derived as follows:                 q _(ijk)=recPicture_(L) [xCb+xB1+k][yCb+yB1+j]                 p _(i,k)=recPicture_(L) [xCb+xB1+k][yCb+yB1−i−1]             -   2. When dE is not equal to 0 and dE is not equal to 3,                 for each sample location (xCb+xB1+k, yCb+yB1), k=0 . . .                 3, the following ordered steps apply:                 -   a. The filtering process for a sample as specified                     below is invoked with the sample values p_(i,k),                     q_(j,k) with i=0 . . . 3, the locations (xP_(i),                     yP_(i)) set equal to (xCb+xB1+k, yCb+yB1−i−1) and                     (xQ_(i), yQ_(i)) set equal to (xCb+xB1+k, yCb+yB1+i)                     with i=0 . . . 2, the decision dE, the variables dEp                     and dEq, and the variable t_(C) as inputs, and the                     number of filtered samples nDp and nDq from each                     side of the block boundary and the filtered sample                     values p_(i)′ and q_(j)′ as outputs.                 -   b. When nDp is greater than 0, the filtered sample                     values p_(i)′ with i=0 . . . nDp−1 replace the                     corresponding samples inside the sample array                     recPicture as follows:                     recPicture[xCb+xB1+k][yCb+yB1−i−1]=p _(i)′                 -   c. When nDq is greater than 0, the filtered sample                     values with j=0 . . . nDq−1 replace the                     corresponding samples inside the sample array                     recPicture as follows:                     recPicture[xCb+xB1+k][yCb+yB1+j]=q _(j)′             -   3. When dE is equal to 3, for each sample location                 (xCb+xB1+k, yCb+yB1), k=0 . . . 3, the following ordered                 steps apply:                 -   a. The filtering process for a luma sample using                     long filters below is invoked with the sample values                     p_(i,k), q_(j,k) with i=0 . . . maxFilterLengthP and                     j=0 . . . maxFilterLengthQ, the locations (xP_(i),                     yP_(i)) set equal to (xCb+xB1+k, yCb+yB1−i−1) and                     (xQ_(j), yQ_(j)) set equal to (xCb+xB1+k, yCb+yB1+j)                     with i=0 . . . maxFilterLengthP−1 and j=0 . . .                     maxFilterLengthQ−1, the variables maxFilterLengthP,                     maxFilterLengthQ, and the variable t_(C) as inputs,                     and the filtered sample values p_(i)′ and q_(j)′ as                     outputs.                 -   b. The filtered sample values p: with i=0 . . .                     maxFilterLengthP−1 replace the corresponding samples                     inside the sample array recPicture as follows:                     recPicture[xCb+xB1+k][yCb+yB1−i−1]=p _(i)′                 -   c. The filtered sample values q_(j)′ with j=0 . . .                     maxFilterLengthQ−1 replace the corresponding samples                     inside the sample array recPicture as follows:                     recPicture[xCb+xB1+k][yCb+yB1+j]=q _(j)′

In one example, a filter process for a luma sample may be as follows:

-   -   Inputs to this process are:         -   the sample values p_(i) and q_(j) with i=0 . . . 3,         -   the locations of p_(i) and q_(i), (xP_(i), yP_(i)) and             (xQ_(i), yQ_(i)) with i=0 . . . 2,         -   a variable dE,         -   the variables dEp and dEq containing decisions to filter             samples p1 and q1, respectively,         -   a variable t_(C).     -   Outputs of this process are:         -   the number of filtered samples nDp and nDq,         -   the filtered sample values and q₁′ with i=0 . . . nDp−1, j=0             . . . nDq−1.             -   Depending on the value of dE, the following applies:         -   If the variable dE is equal to 2, nDp and nDq are both set             equal to 3 and the following strong filtering applies:             p ₀′=Clip3(p ₀−2*t _(C) ,p ₀+2*t _(C),(p ₂+2*p ₁+2*p ₀+2*q ₀             +q ₁+4)>>3)             p ₁′=Clip3(p ₁−2*t _(C) ,p ₁+2*t _(C),(p ₂ +p ₁ +p ₀ +q             ₀+2)>>2)             p ₂′=Clip3(p ₂−2*t _(C) ,p ₂+2*t _(C),(2*p ₃+3*p ₂ +p ₁ +p ₀             +q ₀+4)>>3)             q ₀′=Clip3(q ₀−2*t _(C) ,q ₀+2*t _(C),(p ₁+2*p ₀+2*q ₀+2*q ₁             +q ₂+4)>>3)             q ₁′=Clip3(q ₁−2*t _(C) ,q ₁+2*t _(C),(p ₀ +q ₀ +q ₁ +q             ₂+2)>>2)             q ₂′=Clip3(q ₂−2*t _(C) ,q ₂+2*t _(C),(p ₀ +q ₀ +q ₁+3*q             ₂+2*q ₃+4)>>3)         -   Otherwise, nDp and nDq are set both equal to 0 and the             following weak filtering applies:             -   The following applies:                 Δ=(9*(q ₀ −p ₀)−3*(q ₁ −p ₁)+8)>>4             -   When Abs(A) is less than t_(C)*10, the following ordered                 steps apply:                 -   The filtered sample values p₀′ and q₀′ are specified                     as follows:                     Δ=Clip3(−t _(C) ,t _(C),Δ)                     p ₀′=Clip1_(Y)(p ₀+Δ)                     q ₀′=Clip1_(Y)(q ₀−Δ)                 -   When dEp is equal to 1, the filtered sample value                     p₁′ is specified as follows:                     Δp=Clip3(−(t _(C)>>1),t _(C)>>1,(((p ₂ +p ₀+1)>>1)−p                     ₁+Δ)>>1)                     p ₁′=Clip1_(Y)(p ₁ +Δp)                 -   When dEq is equal to 1, the filtered sample value                     q₁′ is specified as follows:                     Δq=Clip3(−(t _(C)>>1),t _(C)>>1,(((q ₂ +q ₀+1)>>1)−q                     ₁−Δ)>>1)                     q ₁′=Clip1_(Y)(q ₁ +Δq)                 -   nDp is set equal to dEp+1 and nDq is set equal to                     dEq+1.     -   When nDp is greater than 0 and one or more of the following         conditions are true, nDp is set equal to 0:         -   pcm_loop_filter_disabled_flag is equal to 1 and             pcm_flag[xP₀][yP₀] is equal to 1.         -   cu_transquant_bypass_flag of the coding unit that includes             the coding block containing the sample p₀ is equal to 1.     -   When nDq is greater than 0 and one or more of the following         conditions are true, nDq is set equal to 0:         -   pcm_loop_filter_disabled_flag is equal to 1 and             pcm_flag[xQ₀][yQ₀] is equal to 1.         -   cu_transquant_bypass_flag of the coding unit that includes             the coding block containing the sample q₀ is equal to 1.

In one example, a filter process for a luma sample using long filters may be as follows:

-   -   Inputs to this process are:         -   the variables maxFilterLengthP and maxFilterLengthQ,         -   the sample values p_(i) and q_(j) with i=0 . . .             maxFilterLengthP and j=0 . . . maxFilterLengthQ,         -   the locations of p_(i) and q_(j), (xP_(i), yP_(i)) and             (xQ_(j), yQ_(j)) with i=0 . . . maxFilterLengthP−1 and j=0 .             . . maxFilterLengthQ−1,         -   a variable t_(C).     -   Outputs of this process are:         -   the filtered sample values and q; with i=0 . . .             maxFilterLengthP−1,     -   j=0 . . . maxFilterLengthQ−1.     -   The variables refMiddle, refP and refQ are derived as follows:     -   If maxFilterLengthP is equal to maxFilterLengthQ         -   If maxFilterLengthP is equal to 5             refMiddle=(p ₄ +p ₃+2*(p ₂ +p ₁ +p ₀ +q ₀ +q ₁ +q ₂)+q ₃ +q             ₄+8)>>4             Otherwise             refMiddle=(p ⁶⁻ +p ⁵⁻ +p ₄ +p ₃ +p ₂ +p ₁+2*(p ₀ +q ₀)+q ₁             +q ₂ +q ₃ +q ₄ +q ₅ +q ₆+8)>>4     -   Otherwise If ((maxFilterLengthQ is equal to 7 and         maxFilterLengthP is equal to 5) or         -   (maxFilterLengthQ is equal to 5 and maxFilterLengthP is             equal to 7)             refMiddle=(p ₄ +p ₃+2*(p ₂ +p ₁ +p ₀ ++q ₁ +q ₂)+q ₃ +q             ₄+8)>>4     -   Otherwise If ((maxFilterLengthQ is equal to 5 and         maxFilterLengthP is equal to 3) or         -   (maxFilterLengthQ is equal to 3 and maxFilterLengthP is             equal to 5)             refMiddle=(p ₃ +p ₂ +p ₁ +p ₀ +q ₀ +q ₁ +q ₂ +q ₃+4)>>3     -   Otherwise If ((maxFilterLengthQ is equal to 7 and         maxFilterLengthP is equal to 3)         refMiddle=(2*(p ₂ +p ₁ +p ₀ +q ₀)+p ₀ +p ₁ +q ₁ +q ₂ +q ₃ +q ₄         +q ₅ +q ₆+8)>>4         Otherwise         refMiddle=(p ⁶⁻ +p ⁵⁻ +p ₄ +p ₃ +p ₂ +p ₁+2*(q ₂ +q ₁ +q ₀ +p         ₀)+q ₀ +q ₁+8)>>4         refP=(p _(maxFilterLengthP−) +p _(maxFilterLengthP-1−)+1)>>1         refQ=(q _(maxFilterLengthQ−) +q _(maxFilterLengthQ-1−)+1)>>1     -   The variables f_(i) and OD, are defined as follows:         -   If maxFilterLengthP is equal to 7             f _(0 . . . 6)={59,50,41,32,23,14,5}             t _(C) PD _(0 . . . 6)={6,5,4,3,2,1,1}         -   Otherwise if maxFilterLengthP is equal to 5             f _(0 . . . 4)={58,45,32,19,6}             t _(C) PD _(0 . . . 4)={6,5,4,3,2}             Otherwise             f _(0 . . . 2)={53,32,11}             t _(C) PD _(0 . . . 2)={6,4,2}     -   The variables g_(i) and t_(C)QD_(j) are defined as follows:         -   If maxFilterLengthQ is equal to 7             g _(0 . . . 6)={59,50,41,32,23,14,5}             t _(C) QD _(0 . . . 6)={6,5,4,3,2,1,1}         -   Otherwise if maxFilterLengthQ is equal to 5             g _(0 . . . 4)={58,45,32,19,6}             t _(C) QD _(0 . . . 4)={6,5,4,3,2}             Otherwise             g _(0 . . . 2)={53,32,11}             t _(C) QD _(0 . . . 2)={6,4,2}             p _(i)′=Clip3(p _(i)−(t _(C) *t _(C) PD _(i))>>1,p _(i)+(t             _(C) *t _(C) PD _(i))>>1,(refMiddle*f _(i)+refP*(64−f             _(i))+32)>>6)             q _(j)′=Clip3(q _(j)−(t _(C) *t _(C) QD _(j))>>1,q _(j)+(t             _(C) *t _(C) QD _(j))>>1,(refMiddle*g _(j)+refP*(64−g             _(j))+32)>>6)     -   where i=0 . . . maxLengthP−1 and j=0 . . . maxLengthQ−1

As described above, a tc offset (e.g., slice_tc_offset_div2) is an offset value that applies to the region of video data that includes a particular sample. Further, JVET-L1001 provides where a tc offset, tcOffsetDiv2, is used to derive the indexTc, which is used for clipping operations and for determining some thresholds. In one example, according to the techniques herein, tcOffsetDiv2, can be modified based on the prediction mode. That is, according to the techniques herein tc offsets tcOffsetDiv2_P and tcOffsetDiv2_Q may be derived. In one example, tcOffsetDiv2_P and tcOffsetDiv2_Q may be derived as follows: tcOffsetDiv2_P=tcOffsetDiv2 tcOffsetDiv2_Q=tcOffsetDiv2 If the block at side P is intra,tcOffsetDiv2_P=tcOffsetDiv2_P−2 If the block at side P is intra,tcOffsetDiv2_Q=tcOffsetDiv2_Q−2 tcOffsetDiv2 is updated to (tcOffsetDiv2_P+tcOffsetDiv2_Q+1)>>1

-   -   Then the indexTc_P is derived by Clip3(0,         MAX_QP+DEFAULT_INTRA_TC_OFFSET,         (iQP+DEFAULT_INTRA_TC_OFFSET*(uiBs−1)+(tcOffsetDiv2_P<<1))) and         indexTc_Q is derived similarly.     -   Where,     -   iQP is the average of QPs at P-side and Q-side,     -   DEFAULT_INTRA_TC_OFFSET is a pre-defused max offset, and     -   uiBs is the boundary strength.

Further, as described above, a t_(C) value may be used as a clipping range parameter and/or as a threshold value. Referring to the table in FIG. 6A, which is used to determine a t_(C) value, as described above, in one example, variables, iTc_P and iTc_Q may be used as a clipping range parameter and/or as a threshold value on the samples at the P-side and Q-side, respectively. In one example, iTc_P and iTc_Q are derived as follows using iIndexTC_P and iIndexTC_Q indices to a table entry: iTc_P=sm_tcTable[iIndexTC_P]*iBitdepthScale; iTc_Q=sm_tcTable[iIndexTC_Q]*iBitdepthScale;

-   -   where,     -   sm_tcTable is the table illustrated in FIG. 6A; and,     -   iBitdepthScale is the bit depth scale. It is defined as         1<<(iInputBitdepth−8), where     -   iInputBitdepth is the input bit-depth of a sample.

As described above, in JEM a QTBT leaf node may be analogous to both a PB and a

TB in ITU-T H.265. That is, a CU corresponds to both a PU and a TU. JVET-L1001 provides the same basic partitioning structure as JEM, however, in JVET-L1001, a CU may be further partitioned into sub-blocks, including sub-blocks which are used for prediction and may be referred to as sub-PUs. Filters designed to deblock both sides of an edge, such as, e.g., the filters in Table 1, filters may be classified as either being a long tap filter or a non-long tap filter with respect to each side. For example, with respect to the filters in Table 1, in one example, the filter (s=7,t=3) may be classified as a P-side long tap filter and as a Q-side non long tap filter. Similarly the filter (s=3,t=7) may be classified as a P-side non long tap filter and as a Q-side long tap filter and the (s=7,t=7) filter may be classified as a P-side long tap filter and as Q-side is long tap filter. When performing deblocking on a boundary, a long tap filter may not be allowed for a side based on one or more of: a sub-block size associated with the side; a distance from an edge to the next parallel deblocking edge; CU size associated with the side; TU size associated with the side; and/or a PU size associated with the side.

Further, when sub-block boundaries are being deblocked and a long tap filter is being employed, a long tap filter may cross sub-block boundaries, which may result in overlap filtering. Overlap filtering may blur textures and may affect parallelization. In one example, according to the techniques herein, a CU with sub-blocks may be treated as a non-large block. That is, in some cases, certain edges associated with a block containing sub-blocks may not be deblocked. In one example, a long tap filter, which as described above, may, in some examples include a filter that modifies and/or has a filter support that includes at least three or more lines, can then only be used on the large block side. It should be noted that in other examples, with respect to sub-blocks, a long tap filter may include any filter that modifies and/or has a filter support that crosses a sub-block boundary. Thus, a filter may be disabled and/or modified anytime it modifies and/or has a filter support that crosses a sub-block boundary support.

In one example, in this case, the bSideQisLargeBlk and bSidePisLargeBlk, described herein, may be modified as follows:

-   -   If the block at P-side of the current boundary(CU boundary or         sub-PU boundary) makes use of sub-blocks, bSidePisLargeBlk is         set to false.     -   If the block at Q-side of the current boundary(CU boundary or         sub-PU boundary) makes use of sub-blocks, bSideQisLargeBlk is         set to false.

In one example, control logic dependent on the bSidePisLargeBlk and bSideQisLargeBlk may remain as provided above. In one example, for luma, if bSidePisLargeBlk is false, a long tap filter and large block logic cannot be used on the P-side and if bSideQisLargeBlk is false, a long tap filter and large block logic cannot be used on the Q-side. It should be noted that although bSidePisLargeBlk and bSideQisLargeBlk are described above with respect to the luma component, bSidePisLargeBlk and bSideQisLargeBlk may be similarly applied for a chroma component based on the number of chroma samples in a block. Thus, in one example, for chroma, bSidePisLargeBlk is TRUE when P-side number of chroma samples is greater than or equal to a threshold (e.g., 8, 16), Otherwise it is FALSE; and bSideQisLargeBlk is TRUE when Q-side number of chroma samples is greater than or equal to a threshold (e.g. 8, 16), Otherwise it is FALSE. If bSidePisLargeBlk or bSideQisLargeBlk are false, a long tap filter cannot be used on the current boundary.

In one example, according to the techniques herein, if the current horizontal boundary is a CTU boundary, and the block at the P-side (and/or Q-side) makes use of sub-PUs, the block at the P-side (and/or Q-side) may be treated as a small block (e.g., a large block determination is set to false). Further, in one example, when a block is treated as a small block, padding may be used on a side where samples span another sub-block region.

In one example, one or more of the following rules may be used to prioritize filtering an outside sub-block edge over an inside sub-block edge:

-   -   For N×N luma grid deblocking, when deblocking inside sub block         edges, if it is possible that the filter support includes         samples that may be deblocked by (parallel) outside sub block         edge deblocking, then do not deblock that edge using that         filter. For example, if the distance is less than a threshold         (e.g., 4, 8) for luma, then do not allow use of subset of         filters. In an example a subset of luma long filter e.g., subset         of {(s=7,t=7) (s=7,t=3) (s=3,t=7)} may not be allowed if their         filter support may include samples that may be deblocked. In an         example, HEVC strong filter HEVC_P, HEVC_Q may not be allowed if         their filter support may include samples that may be deblocked.     -   For N×N luma grid deblocking, when deblocking inside sub block         edges, if it is possible that the control decision process uses         samples that may be deblocked by (parallel) outside sub block         edge deblocking, then either alter the control process to not         make use of such samples or skip deblocking of the edge.     -   For N×N chroma grid deblocking, when deblocking inside sub block         edges, if it is possible that the filter support includes         samples that may be deblocked by (parallel) outside sub block         edge deblocking, then do not deblock that edge using that         filter. For example, if the distance is less than a threshold         (e.g., 4, 8) or chroma, then do not allow use of chroma long         filter e.g., HEVC_P, HEVC_Q, CL_P, CL_Q.     -   For N×N chroma grid deblocking, when deblocking inside sub block         edges, if it is possible that the control decision process uses         samples that may be deblocked by (parallel) outside sub block         edge deblocking, then either alter the control process to not         make use of such samples or skip deblocking of the edge.     -   For N×N luma grid deblocking, when deblocking inside sub block         edges, if it is possible that the deblocked samples (i.e.         samples that may change value) are included in filter support or         control process of the (parallel) outside edge, then do not         deblock that edge. For example, if the distance of inside sub         block edge from the parallel outside edge is less than a         threshold (e.g., 4, 8).     -   For N×N chroma grid deblocking, when deblocking inside sub block         edges, if it is possible that the deblocked samples (i.e.         samples that may change value) are included in filter support or         control process of the (parallel) outside edge, then do not         deblock that edge. For example, if the distance of inside sub         block edge from the parallel outside edge is less than a         threshold (e.g., 4, 8).

It should be noted that in the examples, above, in some examples, N may be 4 or 8.

In one example, deblocking of sub block edges aligned with transform edges may be prioritized. For example, if a transform edge deblocking may alter any of the samples that can be used in the filter support and/or decision process of another (e.g., parallel) sub block edge, then the sub block edge is not deblocked (i.e., to enable parallelization).

Examples of a CU including sub blocks include the following: a 128×128 CU including four 64×64 sub-PUs, a 128×64 CU including two 64×64 sub-PUs, and a 64×128 CU including two 64×64 sub-PUs. As provided by the example rules above, in some examples, sub-PU edges inside the CU may include filter support or a control decision samples, that may be altered by long filter, and as such, in some cases, these edges may not be deblocked, even if they would otherwise align with a deblocking grid.

In one example, when transform coefficients are not present (e.g., transform coefficients do not include any non-zero values) for a CU containing sub-PUs, CU is deblocked according to any of the techniques provided above for cases of a deblocking a CU containing sub-PUs, and when coefficients are present, the CU is deblocked as if the CU does not contain sub-PUs.

It should be noted that according to the techniques herein, when determining the size of a CU for purposes of deblocking a sub-PU size (or other sub-block size) may be used instead. For example, when considering the boundary between two 64×64 CUs, if one of the CUs contained 8×8 sub-PUs, the boundary may be considered as if there was a 64×64 CU on one side and 8×8 CUs on the other side. Similarly, chroma components may be considered in a similar manner.

Referring again to FIG. 8 , entropy encoding unit 218 receives quantized transform coefficients and predictive syntax data (i.e., intra prediction data and motion prediction data). It should be noted that in some examples, coefficient quantization unit 206 may perform a scan of a matrix including quantized transform coefficients before the coefficients are output to entropy encoding unit 218. In other examples, entropy encoding unit 218 may perform a scan. Entropy encoding unit 218 may be configured to perform entropy encoding according to one or more of the techniques described herein. In this manner, video encoder 200 represents an example of a device configured to receive an array of sample values including adjacent reconstructed video blocks for a component of video data, and modifying sample values in the adjacent reconstructed video blocks according to multiple passes of a deblocking filter.

Referring again to FIG. 7 , data encapsulator 107 may receive encoded video data and generate a compliant bitstream, e.g., a sequence of NAL units according to a defined data structure. A device receiving a compliant bitstream can reproduce video data therefrom. Further, a device receiving a compliant bitstream may perform a sub-bitstream extraction process, where sub-bitstream extraction refers to a process where a device receiving a compliant bitstream forms a new compliant bitstream by discarding and/or modifying data in the received bitstream. It should be noted that the term conforming bitstream may be used in place of the term compliant bitstream.

Referring again to FIG. 7 , interface 108 may include any device configured to receive data generated by data encapsulator 107 and transmit and/or store the data to a communications medium. Interface 108 may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can send and/or receive information. Further, interface 108 may include a computer system interface that may enable a file to be stored on a storage device. For example, interface 108 may include a chipset supporting Peripheral Component Interconnect (PCI) and Peripheral Component Interconnect Express (PCIe) bus protocols, proprietary bus protocols, Universal Serial Bus (USB) protocols, I²C, or any other logical and physical structure that may be used to interconnect peer devices.

Referring again to FIG. 7 , destination device 120 includes interface 122, data decapsulator 123, video decoder 124, and display 126. Interface 122 may include any device configured to receive data from a communications medium. Interface 122 may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can receive and/or send information. Further, interface 122 may include a computer system interface enabling a compliant video bitstream to be retrieved from a storage device. For example, interface 122 may include a chipset supporting PCI and PCIe bus protocols, proprietary bus protocols, USB protocols, I²C, or any other logical and physical structure that may be used to interconnect peer devices. Data decapsulator 123 may be configured to receive and parse any of the example parameter sets described herein.

Video decoder 124 may include any device configured to receive a bitstream and/or acceptable variations thereof and reproduce video data therefrom. Display 126 may include any device configured to display video data. Display 126 may comprise one of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display. Display 126 may include a High Definition display or an Ultra High Definition display. It should be noted that although in the example illustrated in FIG. 7 , video decoder 124 is described as outputting data to display 126, video decoder 124 may be configured to output video data to various types of devices and/or sub-components thereof. For example, video decoder 124 may be configured to output video data to any communication medium, as described herein.

FIG. 9 is a block diagram illustrating an example of a video decoder that may be configured to decode video data according to one or more techniques of this disclosure. In one example, video decoder 300 may be configured to decode transform data and reconstruct residual data from transform coefficients based on decoded transform data. Video decoder 300 may be configured to perform intra prediction decoding and inter prediction decoding and, as such, may be referred to as a hybrid decoder. In the example illustrated in FIG. 9 , video decoder 300 includes an entropy decoding unit 302, inverse quantization unit 304, inverse transform coefficient processing unit 306, intra prediction processing unit 308, inter prediction processing unit 310, summer 312, filter unit 314, and reference buffer 316. Video decoder 300 may be configured to decode video data in a manner consistent with a video coding system. It should be noted that although example video decoder 300 is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video decoder 300 and/or sub-components thereof to a particular hardware or software architecture. Functions of video decoder 300 may be realized using any combination of hardware, firmware, and/or software implementations.

As illustrated in FIG. 9 , entropy decoding unit 302 receives an entropy encoded bitstream. Entropy decoding unit 302 may be configured to decode syntax elements and quantized coefficients from the bitstream according to a process reciprocal to an entropy encoding process. Entropy decoding unit 302 may be configured to perform entropy decoding according any of the entropy coding techniques described above. Entropy decoding unit 802 may determine values for syntax elements in an encoded bitstream in a manner consistent with a video coding standard. As illustrated in FIG. 9 , entropy decoding unit 302 may determine quantized coefficient values and predication data from a bitstream. In the example illustrated in FIG. 9 , inverse quantization unit 304 receives quantized coefficient values and outputs transform coefficients. Inverse transform processing unit 306 receives transform coefficients and outputs reconstructed residual data.

Referring again to FIG. 9 , reconstructed residual data may be provided to summer 312. Summer 312 may add reconstructed residual data to a predictive video block and generate reconstructed video data. A predictive video block may be determined according to a predictive video technique (i.e., intra prediction and inter frame prediction). Intra prediction processing unit 308 may be configured to receive intra prediction syntax elements and retrieve a predictive video block from reference buffer 316. Reference buffer 316 may include a memory device configured to store one or more frames of video data. Intra prediction syntax elements may identify an intra prediction mode, such as the intra prediction modes described above. Inter prediction processing unit 308 may receive inter prediction syntax elements and generate motion vectors to identify a prediction block in one or more reference frames stored in reference buffer 316. Inter prediction processing unit 310 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used for motion estimation with sub-pixel precision may be included in the syntax elements. Inter prediction processing unit 310 may use interpolation filters to calculate interpolated values for sub-integer pixels of a reference block.

Filter unit 314 may be configured to perform filtering on reconstructed video data. For example, filter unit 314 may be configured to perform deblocking and/or Sample Adaptive Offset (SAO) filtering, e.g., based on parameters specified in a bitstream. Further, it should be noted that in some examples, filter unit 314 may be configured to perform proprietary discretionary filtering (e.g., visual enhancements, such as, mosquito noise reduction). Filter unit 314 may operate in a similar manner to filter unit 216. As illustrated in FIG. 9 , a reconstructed video block may be output by video decoder 300. In this manner, video decoder 300 may be configured to receive an array of sample values including adjacent reconstructed video blocks for a component of video data and modify sample values in the adjacent reconstructed video blocks according to multiple passes of a deblocking filter.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

Moreover, each functional block or various features of the base station device and the terminal device used in each of the aforementioned embodiments may be implemented or executed by a circuitry, which is typically an integrated circuit or a plurality of integrated circuits. The circuitry designed to execute the functions described in the present specification may comprise a general-purpose processor, a digital signal processor (DSP), an application specific or general application integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic, or a discrete hardware component, or a combination thereof. The general-purpose processor may be a microprocessor, or alternatively, the processor may be a conventional processor, a controller, a microcontroller or a state machine. The general-purpose processor or each circuit described above may be configured by a digital circuit or may be configured by an analogue circuit. Further, when a technology of making into an integrated circuit superseding integrated circuits at the present time appears due to advancement of a semiconductor technology, the integrated circuit by this technology is also able to be used.

Various examples have been described. These and other examples are within the scope of the following claims.

CROSS REFERENCE

This Nonprovisional application claims priority under 35 U.S.C. § 119 on provisional Application No. 62/767,362 on Nov. 14, 2018, No. 62/790,917 on Jan. 10, 2019, No. 62/793,844 on Jan. 17, 2019, the entire contents of which are hereby incorporated by reference. 

The invention claimed is:
 1. A method of filtering reconstructed video data, the method comprising: receiving an edge type variable specifying whether a vertical edge or a horizontal edge is being filtered in a current block of the reconstructed video data; deriving a maximum filter length of a deblocking filter based on the edge type variable and one or more conditions relating to at least one of a size of a transform block associated with the current block or a size of an adjacent transform block, wherein: when the edge type variable specifies that the vertical edge is filtered, the size of the transform block associated with the current block is a horizontal width of the transform block associated with the current block and the size of the adjacent transform block is a horizontal width of the adjacent transform block, and when (i) the edge type variable specifies that the horizontal edge is filtered and (ii) a remainder of a vertical location of the horizontal edge divided by a height of a coding tree block is equal to 0, the maximum filter length is set to 1; and performing a deblocking filtering, by the deblocking filter, on the current block of the reconstructed video data based on the maximum filter length, wherein a value of a luma filtered sample in the current block is clipped based on a position of the luma filtered sample.
 2. The method of claim 1, wherein the maximum filter length is set to 7 when (i) the edge type variable specifies that the horizontal edge is filtered and (ii) a vertical height in luma samples of the transform block associated with the current block is equal to or greater than
 32. 3. The method of claim 2, wherein the maximum filter length is set to 3 when (i) the edge type variable specifies that the horizontal edge is filtered and (ii) the vertical height in luma samples of the transform block associated with the current block is less than
 32. 4. The method of claim 1, wherein the maximum filter length is set to 3 when (i) the edge type variable specifies that the horizontal edge is filtered and (ii) a first vertical height of the transform block associated with the current block at a chroma location in the current block and a second vertical height of the adjacent transform block are both equal to or greater than
 8. 5. The method of claim 4, wherein the maximum filter length is set to 1 when the edge type variable specifies that the horizontal edge is filtered and at least one of (i) the first vertical height of the transform block associated with the current block at the chroma location in the current block or (ii) the second vertical height of the adjacent transform block is less than
 8. 6. The method of claim 1, wherein the maximum filter length is set to 7 when (i) the edge type variable specifies that the vertical edge is filtered and (ii) a horizontal width in luma samples of the transform block associated with the current block is equal to or greater than
 32. 7. The method of claim 6, wherein the maximum filter length is set to 3 when (i) the edge type variable specifies that the vertical edge is filtered and (ii) the horizontal width in luma samples of the transform block associated with the current block is less than
 32. 8. The method of claim 1, wherein the maximum filter length is set to 3 when (i) the edge type variable specifies that the vertical edge is filtered and (ii) a first horizontal width in chroma samples of the transform block associated with the current block at a chroma location in the current block and a second horizontal width in chroma samples of the adjacent transform block are both equal to or greater than
 8. 9. The method of claim 8, wherein the maximum filter length is set to 1 when the edge type variable specifies that the vertical edge is filtered and at least one of (i) the first horizontal width in the chroma samples of the transform block associated with the current block at the chroma location in the current block or (ii) the second horizontal width in the chroma samples of the adjacent transform block is less than
 8. 10. The method of claim 1, wherein, when the edge type variable specifies that the horizontal edge is filtered, the size of the transform block associated with the current block is a vertical height of the transform block associated with the current block and the size of the adjacent transform block is a vertical height of the adjacent transform block.
 11. The method of claim 1, wherein the maximum filter length is derived based on a color component variable specifying a particular color component value for the current block.
 12. The method of claim 1, wherein receiving the edge type variable comprises receiving a tree type variable specifying whether a dual tree is used to partition the reconstructed video data, and wherein deriving the maximum filter length comprises deriving the maximum filter length based on the tree type variable.
 13. The method of claim 1, wherein the maximum filter length for the current block identifies a maximum number of samples from the vertical edge or the horizontal edge to modify when performing the deblocking filtering on the current block.
 14. The method of claim 13, wherein the maximum number of samples from the vertical edge or the horizontal edge to use as inputs when performing the deblocking filtering on the current block is derived from the maximum filter length. 